Keywords

In the discussion of matters pertaining to stem cell transplantation (SCT), especially as a socially situated phenomenon, it is always necessary to abandon a singular perspective in favour of bringing empirical, biological and bioethical insights into conversation. In crossing the boundaries between those familiar forms of enquiry, I want to explore and reflect on some recent concerns in the realm of biophilosophy. My own approach to SCT is solidly related to my involvement in a collaborative heart transplantation project that sprang from my identification as a body theorist with a strong commitment to postconventional philosophy and critical cultural theory. Solid organ grafts are materially very different to bone marrow transplants but there is considerable overlap in the phenomenological aspects of the procedure as it differentially affects recipients, donors, and families alike. Questions of identity, of gifting, and of mortality abound, and in kin SCT where the whole process happens within the complex relationships of a single unit, the intertwined impact on lived experience is highly concentrated.

A great deal of empirical research is already to hand around the topic of transplantation – though not so much in relation to SCT – both in strictly biomedical texts that have little place for speculation on the implications of the results and in the social sciences, which are generally more open to providing a theoretical approach to research data. But beyond that, the systematic enquiry into reported lived experience requires, I think, a philosophical approach to complement the sociological and biomedical material. Rather than relying on an additive model to produce new knowledge, what is required is a mode of analysis that intends to interweave many areas of expertise – social, biomedical, legal, psychological – with diverse methodologies that reflect the complexity of the object of enquiry,Footnote 1 in this case SCT involving siblings. In looking at everything involved in the understanding of SCT – the biomedical procedure, the individual and collective experiences of the family, the data collected, the expertise and expectations of the researchers, and the varying analyses applied – what emerges is a knowledge assemblage. That term reflects my own methodological approach in this chapter and views the significance of transplantation itself through the framework of Deleuzian assemblage.Footnote 2

Like heart transplantation, the event of a bone marrow transplant – which is the main form of stem cell transplant under consideration here – speaks to a radical encounter between self and other, and is the site where the conventional boundaries of what constitutes a singular self are deeply problematised. In the case of living kin donation, with which the umbrella project on SCT and the child’s well-being is concerned, the collision of life and death is less prominent than it might be in other scenarios, but nevertheless provides the underlying motivator for action. What I want to focus on is that in the experience of stem cell transplant, the relation of self to other is no longer binary but also reflects an irreducible intertwining that produces a somewhat unstable sense of self for both recipient and donor. At very least, and whatever the empirical connection between the two, the procedure and its aftermath is shot through with some ontological uncertainty. For recipients of donor stem cells, the lived experience arouses complex emotions, not only about the relation between self and the other, but also about the presence of the other within the self. In a powerful way it is a relationship of hybridity, or even spectrality in the philosophical sense intended by Jacques Derrida.Footnote 3 Of course any exercise in life-saving procedure, which SCT may be, raises awareness of personal mortality, insofar as biotechnologies increasingly intervene into terminal conditions that once seemed natural and inevitable. As with other types of transplantation, success in averting death is relatively high, so that the hope for better health and prolonged life is soundly based, albeit living on is not as unproblematic as might be expected. Both recipients and their sibling donors may be significantly disturbed by the procedure, but are afforded little opportunity to explore and try to make sense of any negative emotions that they may experience. As some of the project transcripts make clear, this seems particularly to be the case in the context of intra-familial donation, where the well-being of the family as a unit may be privileged above individual disturbance.Footnote 4 Given, moreover, that the transaction is between siblings, the majority of whom were children at the time, the imposition of a unified narrative of hope might be even harder to resist.

F: [T]hat what’s nice about the whole thing, that a family like that can solve something like this, these problems. (Kötter, father, 130)

Stem cell donation rightly generates public debate around questions of consent and the exploitation of so-called spare parts, but what are given far less time are the wider ethical and philosophical implications of incorporating another’s genetic material. Based on my own participation in a multi-dimensional research project on heart transplantation – The Process of Incorporating a Transplanted Heart (PITH)Footnote 5 – I believe those aspects should be a site of specific attention and perhaps merit primary concern, particularly in the context of the emergent understanding of the phenomenon of microchimerism, which I will go on to explore in detail. There is little doubt that all organic transfer is symbolically complex, such that stem cell donation – like other forms – swiftly moves beyond the functional repair or spare parts metaphor and may seem to constitute the gift of life (though few of the respondents in the SCT project explicitly referred to the transfer as such). Nonetheless, the seemingly laudable metaphor of the gift frequently underlies family understanding of the process, but it raises its own problems and specifically amplifies the potential disturbance to the relation between self and other. Moreover, unlike the case of deceased organ donation – as with heart transplantation – where the spare parts discourse is positively encouraged as less disturbing, in scenarios where there are living familial donors – as in SCT – the reverse is true and the notion is silenced as being highly insensitive. But whichever the type under consideration, few of those intimately involved feel the transaction to be a simple replacement of faulty components for better-working ones. Far from being a neutral and depersonalised procedure, or even the expression of disinterested altruism, the organic material takes on the sense of a real and symbolic gift that binds the giver and receiver together in an economy of exchange. Respondents do not need to be familiar with Marcel Mauss’ theory of the gift (1990) to recognise that the transplanted object carries with it intangible aspects of the other and expectations of reciprocity. The often burdensome but usually inexpressible relation between the two parties centres on the discourse of having been given something precious, the acceptance of which generates certain supposed obligations to the donor.

At the same time, the relation between recipient and donor is more or less existentially loaded in terms of personal identity, as is plainly exemplified in many of the SCT transcripts. The Wahl family mother remarks of her recipient son: “it is something (…) something (…) VERY existential and important for him, that it’s also from his SISTER, because actually he is very attached to her and even more because of this” (65), while the Rohde donor reflects: “now my sister is (laughs), yes, the same as me, how stupid, now I’m no longer unique or something” (102). In the field of heart transplantation, very few of the respondents gave extravagant accounts of felt changes to their sense of personhood, but many felt themselves to be no longer the people they had previously been, in tastes, temperament or behaviour. The researchers in the stem cell study suggest that it is having a close knowledge of the donor – who is after all a sibling relation – that generates such disturbing reflections, but research in the wider field of organ donation shows that complete anonymity is no bar to speculation about hybrid identities (Kaba et al. 2005; Poole et al. 2009). The ontological question ‘Who am I now?’ is a central concern in either case. Although the degree of palpable distress expressed by heart recipients in their newly embodied states was more strongly evident (Poole et al. 2009), it is clear that many stem cell recipients too felt themselves now entangled with the donors beyond the level usually expected of siblings. Certainly there were deep feelings of obligation, or perhaps even guilt in that the prolongation of their own lives depended on not just generosity but the potential discomfort and anxiety endured by very specific others, but it is the intimation of shared attributes that is the most remarkable. In the Spiedal family mother’s account: “it was like this, he [the recipient] gets his brother’s blood, so he BECOMES his brother” (26), while the recipient himself confirms her view: “I mean, I dunno, it’s just a feeling, you’ve got your brother’s blood actually IN you. Like and, mh, yes, it’s FUNNY to describe. It’s as if you were linked even more closely than you would be anyway” (31–32).

The empirical findings from the SCT study interviews reiterate that the experience of bone marrow transplantation can indeed invoke an unfamiliar sense of hybridity. The initial understanding of that disturbance relies on the phenomenological claim that as the self is always embodied, then any changes to the corporeality of an individual must unsettle any stable and fixed sense of self (Merleau-Ponty 1962). The coming together, then, of self and other in the material form of transplantation is no simple matter, but an enterprise of high affective significance. The dominant psycho-social imaginary of the Western world rests on the boundedness and singularity of each individual, so it is hardly surprising that the tangible experience of what is in effect a form of hybridity remains a largely alien perception. Going further, I suggest that considerations of microchimerism at the cellular level introduce new dimensions to the issue of identity, in that the continuing circulation and operation of ‘alien’ genetic material in the peripheral blood supply inevitably raises questions regarding the singularity of the self.

Before coming to the specific nature of microchimerism and its implications in transplantation, I want to look more generally at some of the other elements of stem cell donation that are not readily apparent to those involved on either side. What the PITH project has consistently shown (Abbey et al. 2009) – and we can reasonably speculate that similar forces are at work in stem cell transplants – is that the authorised discourse endlessly reiterated in the clinic and in the media acts to discredit or silence alternative narratives. Questions of hybridity, and the more so regarding chimerism, are clearly discouraged such that those involved may find little support or acknowledgment of the challenging concerns arising from their phenomenological experience post-transplant. As with organ transplantation, and prior to any clinical procedure, the focus for both those choosing to donate and those waiting to receive a stem cell donation, and for the wider families, is likely to be primarily on the prospective health benefits or risks. Yet at the same time, popular media representations of transplantation – though usually around more tangible elements such as heart, eyes or hands – abound with unsettling narratives that suggest an underlying fear that the personal characteristics of the donor might transfer to the recipient, or that s/he (the donor) might reappear as a spectral presence. It goes further than the phenomenological sense that corporeal changes – here the assimilation of donor material – may induce the emergence of a new embodied self, to speak instead of a self haunted as it were by traces of the other. For the majority of the recipients in the PITH study, whose biomedical recovery and well-being was expected to be coincident with a restored sense of singular selfhood, the path to the ontological state of well-Being was often challenging and sometimes impossible. The philosopher Jean-Luc Nancy (2002), who received a donor heart, speaks, for example, of becoming a stranger to himself, while Francisco Varela who had a liver transplant reflects:

We are left to invent a new way of being human where bodily parts go into each other’s bodies, redesigning the landscape of boundaries in the habit of what we are so definitively used to call distinct bodies (2001: 260).

Neither the trope of the spare part nor the expectation of gratitude for the putative gift of life can account for such experiences, and although they provide no direct template for understanding the familial context of sibling donation, there are clearly some similar existential disturbances at stake.

The expectation that SCT enhances health may, then, be somewhat offset by the intuition that there will be a change to the uncomplicated notion of an enduring sovereign self. Such a conception might well be experienced as intrinsically negative for those wedded to the Western logos, but it need not be so. The work of postconventional theorists, such as Jacques Derrida, takes a very different view as it moves away from the trope of singular personhood and individual identity. The insistence of the Western logos on self and other as separate and distinct entities is for Derrida an illusion. As he puts it, the arrival of otherness surprises the host,

enough to call into question, to the point of annihilating or rendering indeterminate, all the distinctive signs of a prior identity, beginning with the very border that delineated a legitimate home and assured lineage (1993: 34),

but that arrival also marks the creative possibility of going beyond the metaphysics of the modernist concept of the self. For Derrida the coming of the other – and we can see it as both abstract and concrete – cannot be denied and it always speaks to a hauntological relationship not just between self and other, but also across past/present/future and between absence and presence, life and death (Derrida 1994). Existence, and that includes personal being-in-the-world, is always dependent on something else that is not present as such, something not graspable in the immediate moment. What matters is that the trace of the unknown other should be openly welcomed (and here we might think of the recipient’s embrace of donor material), not in the expectation that we will benefit – for that can never be certain – but as a way of securing a future.

There is very little in Derrida’s work that refers directly to transplantation but his largely theoretical ‘logic of the supplement’ is clearly of relevance. As with every form of augmentation or supplementation, the prosthetic nature of any transplant positions it as a vital element, not of a predetermined and settled being, but of a creative becoming. In letting go of the illusion of an unchanging, or at least restored, self, it becomes possible to accept the embodied hybridity that transplantation entails in a more welcoming and expansive way. The relation between self and other is no longer binary, still less antagonistic, but becomes entangled – “the guest becomes the host’s host” as Derrida (2000: 125) puts it – and in the PITH project at least, the empirical material showed that those who comprehended the putative loss of corporeal singularity, who did not fetishize autonomy, were less unsettled by their unfamiliar experiences and affects. The recognition that transplantation – whether of a heart or bone marrow – promises restoration but more generally delivers unease speaks to a present reality for many recipients, and indeed the wider families, but, I would argue, a radical rethinking of the nature of embodiment could open up to more liveable alternatives. While the intimate encounters inherent in transplantation processes may provoke feelings of disturbance and anxiety, it is also the point at which we might rethink the temporal and spatial boundaries of all embodiment. I want, then, to explore another, related approach that brings together the philosophy of Gilles Deleuze and Félix Guattari – which pushes Derrida’s insights further towards the existential state of becoming – with some contemporary developments in bioscience. It is here that the recent upsurge of biophilosophical interest in microchimerism becomes significant as that biomedical state plays into, and mirrors, on a very material biological basis, the central Deleuzian concept of assemblage.

Until the late twentieth century, the phenomenon of microchimerism was little known or researched, even in biological science. The term refers to a form of chimerism that operates specifically at the cellular level, unlike its broader meaning, which has its direct origins in Greek myth and figures a combination of body parts from two or more different animal species. Microchimerism denotes the existence – usually in very low concentrations – of what are identified as non-self cells with their own distinct sets of DNA and associated antigens, which arise from different individuals but are present in a single body. Although the terms hybridity and chimerism are often used interchangeably, there is a material difference in that the putatively non-self cells of microchimerism are not assimilated to achieve new uniformity across all cells, but remain distinct. Bioscientific understanding and explanations for the phenomena of both chimerism and microchimerism are uncertain, but the implication is that the conventional model of biologically distinct entities – whether as plants, invertebrates or mammals – where each individual organism is regulated by a single unvarying genome and displays genetic homogeneity across all cells of the body may be unfounded (Nelson 2012). The known circumstances of human microchimerism may indicate a natural state, as in the in utero fusion into a single body of dizygotic twins or the now widely acknowledged phenomenon of foetal cell engraftment into the maternal body, and vice versa. There are also many iatrogenic causes arising from biomedical interventions into the body, such as organ or stem cell transplantations. There are few observable morphological distinctions or evidence of external effects arising from the diverse DNA markers in natural microchimerism, so the actual extent of the condition is unknown. Nonetheless, microchimerism is now accepted – after decades of disparagementFootnote 6 – as a relatively common, and probably ubiquitous phenomenon, but one that is still largely unheeded in the absence of disease or ill-health.

Despite the low incidence of non-self cells, there are compelling reasons to believe that microchimerism is strongly enmeshed with the biomedical outcomes of many transplant procedures, and it is central for bone marrow transplants, where what might be more accurately called macrochimerism is the desired outcome. Most forms of transplant have yielded evidence that the donor DNA enters and circulates in the peripheral blood supply, thus maintaining a consistent presence of genetically divergent cells throughout the body. And occasionally microchimeric cells may accumulate at specific sites such as solid organs (other than the transplant organ itself), again resulting in distinctive instances of macrochimerism. Within immunology and transplant research there is an ongoing and highly oppositional debate with regard to the potential of beneficial or pathological outcomes in the presence of such chimerism, with much research investigating its possible, but as yet unrealised, therapeutic capacity as a counter to allorejection. What is striking, then, is that unlike the situation with solid organ transplants, where the authorised clinical narrative still insists that the DNA of the graft will remain in situ and play no part in recovery and future life (even though that claim is increasingly shown to be an illusion), the biomedical point of stem cell transplants is exactly the opposite. The explicit aim is to import active components that will both replace the originary stem cells, damaged, for example, by treatment for leukaemia, and boost the recipient’s immunological responses. Where existing bone marrow has been fully or partially ablated, the primary intention is to stage a replacement with non-self cells.

In the biomedical context of transplantation, the concerns around microchimerism are less to do with ‘alien’ DNA than with its input to and effect on the immunological status of the recipient. Immediately following the transplant procedure, a regimen of immunosuppressant drugs is established, not just to aid short-term recovery, but sometimes over a lifetime to ensure continuing survival. Left to itself, the recipient’s natural immune response to the unfamiliar donor cells – which carry their own distinctive Human Leucocyte Antigen (HLA) profile – would be an overwhelming onslaught on the putative intrusion, and rejection of the transplanted tissue, resulting in the recipient’s further decline. Where it is possible, as in some kidney transplants and certainly in bone marrow transplantation, careful tissue matching between closely related donor and recipient can eliminate some of the problem. In the case of sibling donation, as in the present study, the parents and children involved express a strong psycho-social desire to keep the whole experience within the family, but that in any case is the preferred medical approach. Nonetheless, there is rarely a complete correspondence of HLA, which is highly specific to each individual, so the resulting histo-incompatibility that would prevent successful grafting is usually controlled by suppressing the recipient’s own antigens. At the same time, a parallel problem arises as the donor cells mobilise a similar rejection response against the recipient. In what is called graft v. host disease, the functional immune markers of the transplant material recognise the non-self status of the recipient and attack the host who may have little defence, especially if already immunocompromised. The biomedical procedure of stem cell transplant is not especially risky in itself: the danger, as in all transplantation interventions, lies in effectively managing the incompatible HLA systems. Although post-transplant care and drug regimens may change over time, the underlying doxa remains the same – that the immune system of all animals naturally operates on the principle of self/non-self discrimination such that donor and recipient antigens are in an antagonistic relation. The success of transplantation procedures, including SCT, is therefore thought to devolve on a successful suppression of the otherwise inevitability of histo-incompatibility. In an interesting twist, peculiar to bone marrow infusions, that suppression may depend on promoting a complete engraftment of donor cells in order to directly counter certain existing conditions such as leukaemia. The graft versus leukaemia effect is a well-recognised benefit of SCT where the lesion is blood-borne and does not extend to subsequent cancers in other organs and tissues (Kolb 2008; Dickinson et al. 2017).

The militaristic metaphors with which immunology is commonly explained go back to the pioneering work of Frank Macfarlane Burnet and Peter Medawar in the mid twentieth century, which set out the seminal principles for most subsequent research. As they both understood it, the purpose of the immune system is to mobilise in response to the incursion of ‘foreign’ – non-self – antigens by releasing an abundance of biochemical agents that would eliminate the putative threat of otherness. They are credited for firmly establishing the apparently natural conflict of the self/non-self cellular relation,Footnote 7 but what is usually overlooked is that Medawar also identified the phenomenon of post-birth dizygotic twin chimerism in certain cattle known as freemartins, and even very rarely in humans. He recognised it as a form of natural immuno-tolerance, but was unable to move beyond calling such an occurrence a ‘natural accident’ and ‘astonishing’ (Medawar 1960). Instead, his legacy remains the conviction that the protection and maintenance of the boundaries between the supposedly normal self and the intrusive other is a natural function of the healthy body, and that in turn has been the dominant template for transplant medicine. It is only in relatively recent years that attempts to reconceptualise the nature and function of the immune system have emerged. Donna Haraway (1989), Polly Matzinger (2001) and more recently, Thomas Pradeu (2012) are notable here, but their influence is limited, albeit the very success of SCT must raise doubts about the viability of the standard model. The issue is that beyond bioscience itself, the socio-cultural imaginary, of which the biomedical imaginary is a subset, is no less committed to precisely the same core belief in the intrinsic nature of self/non-self conflict. The notion of the self embedded in the Western logos speaks to an atomistic, already complete and defensively bounded entity. Any suggestion, indeed any material research, that the immune systems of the self and its other(s) might ever be cooperative is an insult not just to the basic principles of immunology, but to the very understanding of what constitutes human being.

Once it is accepted that the immunological effects of transplantation extend throughout the body of the recipient, then we are obliged to reconsider the relation between self and other. Given that the DNA – and the associated HLA profile – of the donor circulate in the peripheral blood supply at very least, the issue of hybridity takes on a more radical significance. Even when the finer points of DNA coding are scarcely addressed by either clinicians or their patients, the recipient can no longer claim to be ‘all me’, and the intuition of hybridity is frequently an element in the post-transplantation context. Whatever the clinical narrative around SCT, both sides of the transaction display a feeling that the marrow graft signals that some aspects of a donor are incorporated. In a few cases there is a stronger sense that the particular essence of the donor is evident in the recipient. Hybridity is not a term commonly used in the interviews by either the siblings or their wider families; still less were respondents or donors aware of how circulating donor DNA in effect constitutes a microchimeric environment in the recipient body, yet there is surely a sense that the embodied self has changed. In biomedical terms, what may occur – and it is after all the intention of SCT – is that the donor cells may effect a complete engraftment of the bone marrow and peripheral blood supply, while coexisting with the recipient’s own DNA still present in the epithelial cells, for example. It seems unlikely from the interview material that any of this was discussed as being of particular relevance with the families involved. As the father of family Rohde dismissively remarks, and his is the only direct reference: ‘You know I find the concept so crazy, the doctors are talking about chimerism (…), it’s from //comes from the Greek chimera’ (Rohde, father, 106). For everyone concerned the cogent questions are largely focused on the material consequences of SCT in terms of future health and illness, but the philosophical implications of the coming together of self and other should not be ignored. It is not a case of hybridity as such, which technically indicates a form of assimilation, but precisely of chimerism where – at the cellular level – the incoming components remain genetically distinct.

In solid organ transplantation, the issue of chimerism was first recognised in Edward Starzl’s work in the early 1990s during a retrospective study of the outcome of kidney transplants from almost 3 decades earlier. At that time, effective immunosuppressant drugs were unavailable, so mutual rejection processes between host and donor were uncontrolled. Despite standard biomedical expectation, nonetheless, several recipients had survived. In investigating this puzzling endurance, Starzl showed that donor HLA was not just localised at the site of the transplant organ but could be detected throughout the recipient body (Starzl et al. 1992). Other researchers then demonstrated that cell mobility was bidirectional, with the transplant organs themselves showing evidence of incorporating the existing HLA typing of recipients (Quaini et al. 2002). In short, it was the first clear indication of extensive microchimerism. Starzl proposed that the problem of immunorejection might be countered by keeping a balance between the immunogenetic effects of the two different populations of cells by means of recipients being given pre-treatment infusions of hematopoietic (stem) cells derived from the bone marrow of living donors. His underlying aim was to find a way of minimising the need for highly toxic regimens of immunosuppressant drugs, which can generate a plethora of new morbidities. Because the pre-treatment infusions did not prove reliably effective in solid organ procedures, Starzl’s insights were widely discounted, even though the whole enterprise of SCT shows the potential of microchimerism in relation to immunotolerance. The contemporary absence of discussion about microchimerism among SCT cliniciansFootnote 8 and families is puzzling given that even the briefest online research makes clear that the donor DNA and HLA takes over bone marrow function and circulates in the blood, though on popular sites, there is little recognition that it may equally settle in solid organs and other tissues. One might ask whether the omission of explanatory information about issues that may affect both future health and existential well-Being raises the conventional question of what constitutes informed consent, especially where children are the recipients and donors for whom proxy decisions are made.

Where recognition of iatrogenic microchimerism is still relatively sparse in the clinical discourse, the question of macrochimerism is all but absent. In one notable case reported in 2008, initially in a professional journal and subsequently splashed by the media, the blood group of a 9-year-old female child switched from O-negative to O-positive following an emergency liver transplant, and her immunological profile realigned itself with that of the male deceased donor (Alexander 2008). The realisation that such unexpected and extensive chimerism had occurred resulted in all immunosuppressant medication being withdrawn, enabling the donor cells to rapidly effect a therapeutically beneficial engraftment and facilitating the patient’s full recovery in the absence of drugs. Even though the microchimeric process was relatively well known after liver transplantation, it was believed to be ephemeral and of little consequence; certainly it was not seen as a significant factor in graft acceptance. The case reported by Alexander, however, was not one of simple microchimerism – in which ‘non-self’ cells constitute no more than 1 in 1000 – but of enduring whole-body genetic translocation. The problematic of immuno(in)compatibility is not, however, limited to iatrogenic outcomes, and by exploring the wider context of cellular chimerism it becomes possible to trace its further significance. The incorporation of allogenetic material is one mode of inducing microchimerism but the phenomenon has many other grounds, many of them occurring naturally. Microchimerism in and after pregnancy is now well established and is believed to be frequent and possibly universal (Nelson 2012), and moreover, it may persist for decades, perhaps even indefinitely (Bianchi et al. 1996). A further shock was the discovery by Diana Bianchi’s lab that women who have never been pregnant can also be carrying Y chromosomes, indicating the presence of non-self DNA (Khosrotehrani and Bianchi 2005), and it is now speculated that there are multiple reasons why non-self cells might circulate in the body.Footnote 9 Once microchimerism is established in the body of an individual, the bidirectional cellular traffic across the placental barrier indicates that whatever the initial cause, it will become intergenerational. The implication is that recipient and donor bodies may already be microchimeric, with the transplant material simply adding to the incidence of non-self cells. If indeed such populations of distinct DNA and HLA are durable over and beyond the normal life-course, it is not just our understanding of the immune system that requires revision. The projected ubiquity of such somatic multiplicity and intracorporeal malleability surely poses a fundamental challenge to the Western socio-cultural imaginary of singular selfhood that finds its biological justification in the individual uniqueness of DNA identity.

I turn, now, to a more detailed exploration of how bioscientific doxa around microchimerism could be opened up through a more philosophical critique of the relation between self and other, where the supposed boundaries of the one secure it against the intrusions of others. It is a surprise, as Cohen (2009) makes clear, to find that the original concept of immunity was confined to juridical and political discourse; it was not until the late 19th century that the more familiar biomedical understanding of immunity as a defence system for the body emerged. Contemporary philosophy is highly engaged with the notion and draws on both historical strands. Leaving aside for a moment Derrida’s rethinking of hospitality as a mode that might speak to the nature of microchimerism (Shildrick 2019), the most cogent point of engagement is with philosopher Roberto Esposito’s deconstructive analysis. The term ‘immunity’ may appear to be unrelated in meaning to ‘community’ – where community refers to a group linked together through conditions in common or indicates public ownership, and immunity is an insular attribute of the self – yet Esposito demonstrates that they are inextricably entangled. As he (2008) lays out, both words derive from the Latin term ‘munus’, which indicates an obligation of responsiveness to the other or a gift, such that the one who claims immunity is absolved from the self-abnegation inherent to community and eludes the reciprocity of gifting (Shildrick 2016). The trope of gift giving is ubiquitous in transplantation discourse, where the incorporation of donor material – which currently entails the deliberate suppression of the recipient’s immune system – sets in place an enduring obligation of gratitude. For many that extends to a sense of mutual kinship between recipient and donor following transplant (Shildrick 2013a, b), or even shared identity as in the case of SCT between existing kin (d’Aurio 2015, current study).Footnote 10 Glossing Esposito’s work, Timothy Campbell explains: ‘Accepting the munus directly undermines the capacity of the individual to identify himself or herself as such and not part of the community’ (Campbell 2010: x).Footnote 11 As Esposito recognises, conventional culture cannot tolerate the logic of the two-in-one or the one that becomes two (2008: 168) . Few recipients will think explicitly in such terms but they express precisely what may be disturbing about the transaction: prior to accepting the ‘gift of life’ they have lived as autonomous selves within the normative paradigms of Western modernism, with an unthinking, and probably unexpressed, belief in the corporeal distinction between one self and an other; afterwards the closure of individual identity is no longer possible. Small wonder then that so many of the families involved in the SCT study made a joke of such unsettling intuitions.Footnote 12

Esposito’s primary interest is in theorising biopolitics, but he draws on the materiality of biomedical immunity throughout. As Donna Haraway’s prescient assertion reminds us, immunology is at the heart of biopolitics (Haraway 1989). Esposito also covers some of the same ground as Derrida, who has written extensively on the concept of autoimmunity and whose reworking of the gift and of absolute hospitality, as I briefly mentioned, brings new dimensions of understanding to the nature of transplantation (see Shildrick 2013a). By engaging with both the material and ontological transformations of embodiment, what concerns Esposito is the development of an affirmative biopolitics that goes beyond the neutral biomedical figure of tolerance. In place of a state marked in immunological terms by the absence of reaction to the other, effectively a form of passive coexistence, he wants to postulate a mode of positive relation between self and other. Where the microchimeric outcome of transplantation seems to stage a phenomenological insult to the notion of an individual life restored – given that the differential DNA of the donor cells resist assimilation and remain fundamentally other – Esposito offers instead a logic of dynamic multiplicity where dissimilarity itself is mutually productive. He writes:

we need to find the mode, the forms, the conceptual language for converting the immunitary declension (…) into a singular and plural logic in which the differences become precisely that which keeps the world united. (‘Immunization and Violence’ (n.d.:13))

The notion of a radical hospitality proposed by Derrida (2000) has previously done some of that work in establishing the always/already interiority of otherness, but it is less directed towards an explicitly transformative and creative end. Esposito more clearly takes his lead from Deleuze, for whom the key purpose of philosophy is to enable new modes of thinking that will facilitate more adequate ways of conceptualising the events that transform life. Deleuze has little interest – even in a deconstructive mode – in modernist semantics that focus on individual and autonomous selfhood; rather he recognises not simply the one in the other, but the modality of an impersonal vitalism that eschews the limitations of being and privileges instead the excessive potentiality of life’s becoming. In conclusion, then, I offer some brief speculations on how the significance of chimerism might be read through a Deleuzian approach that takes for granted the illusory nature of self-other distinctions.

As with Derrida, Deleuze (both alone and in collaboration with Guattari) decisively breaks away from modernist thought, not only in contesting singular embodiment per se, but in opening up the disturbing ontological question ‘Who am I?’ that so clearly underlies the unease generated by the transplant exchange. It marks a fundamental challenge to the conventional paradigm of ‘self versus other’ that still – despite recent research discoveries around microchimerism – dominates the bioscientific discourse of immunology and the socio-cultural imaginary more widely, and an emerging theoretical shift to an understanding of the normal ‘self’ as constitutively chimeric. The Deleuzian rejection of the notion of an atomistic and sovereign subject of modernity, with an enduring sense of self, does not entirely deny the experience of individuality but sees it as at most provisional and always within a process of unravelling. In place of static ‘being’, the emphasis is on a state of becoming (Deleuze and Guattari 1987). The unique experiences and putatively contained embodiment of each person are enmeshed in what Deleuze calls assemblages, those multifarious and impermanent webs of interconnections that generate dynamic fields of energy. Life itself is an unlimited vitalist force that exceeds the individual life-span from birth to death (see Braidotti 2006; Shildrick 2013b). The concept of assemblages provides a convincing alternative to the logic of unity and wholeness, and a perspective from which to understand what is at stake in chimerism, which although not a term used by Deleuze has a similar import. To recap, chimerism – whether of whole parts or of cellular material – denotes not a simple assimilation that overrides the original differences, but a conjunction of disparate elements that both deform and reorganise each other, yet are still functional within a newly configured relationship. It is a way of thinking about human life as always and inextricably entangled not only with other organisms but with an assembly of technologies and processes, and that is precisely what transplantation exemplifies.

At a less rarefied level we might also think about the family itself as an assemblage – a coming together of individuals who in certain circumstances function as a conglomeration rather than as autonomous beings. Certainly the familial bodies at the focus of the SCT research project seem to take that view, and although they may be open to the changes wrought by events and processes and do not cleave to a static essence, there is still a strong commitment to an organised and organising intra-related entity. As the Bahr family mother commented: ‘Something very special connects us, what we experienced together, what we endured and survived. That continues to connect us, you know’ (89). It clearly matters to the members that they are seen as a family and that the fluid circumstances in which they find themselves can be managed within the unit. In that sense they satisfy the English language definition of assemblage as the fitting together of disparate parts to form a unified whole, but not the full Deleuzian sense in which the original word agencement indicates a loosely linked array of heterogeneous elements (Nail 2017).Footnote 13 Nonetheless, both the family as some kind of limited assemblage, and the nexus of chimerism, which they are implicitly obliged to accept, express the constructive power of interconnection and the ceaseless processes of transformation. The concepts of both assemblage and chimerism may help us to rethink transplantation, not as a singular and time-limited event leading ideally to restoration of the status quo, but as a continuing project for both the recipient and the donor. For Deleuze, human life is not limited to the temporal frame marked out by the conventional life-span of any individual, but rather persists as one variable element of the enveloping cycle of becoming that constitutes all types of living (and dead) organisms and machines. For all of us, the personal life course is undeniably marked by discrete episodes such as pregnancy, trauma, or transplantation itself, where there are tangible changes or transformations, yet in another dimension, events are also atemporal and intangible forces and points of intensity that are excessive to any singular or fixed form of embodiment. The science and politics of immunity that operate in terms of protection of singularity and the management of boundaries between self and other are superseded by the assemblage of communal becoming.

In the immediate and conventional context of SCT procedures – in which the individuality of each person is taken for granted – the point is to restore the prospective recipient to the self who preceded illness and the specific biomedical procedure. In contrast, Deleuzian philosophy contests any notion of the individual ‘ownership’ of embodied life and promotes instead an appreciation of the intensity of ongoing becoming in a process without beginning or end (Braidotti 2006). In any case, what matters for Deleuze is not whether the recipient re-establishes functional efficacy, the prospect of an extended life, or even ontological security, but what Rosi Braidotti calls ‘sustainability’:

The sustainability of these futures consists in their being able to mobilize, actualize and deploy cognitive, affective and collective forces which had not so far been activated…These forces concretize in actual, material relations and can thus constitute a network, web or rhizome of interconnection with others. (Braidotti 2010: 413)

The science and politics of immunity that operate in terms of the protection of singularity and the management of boundaries between self and other is superseded by the assemblage of productive becoming. The recipient and donor in such an assemblage are no longer positioned as self and other, but are components of an apersonal correlation of elements that reflects the materiality of the unseen cellular chimerism that the biomedical procedures have mobilised. In addition to the predictable and desired changes that result from SCT, like the recovery of health, the overlooked transmutations effected by microchimerism must inevitably disorder existing corporeal boundaries. The authoritative discourse of conventional biomedicine that mirrors the modernist socio-political objective of maintaining the illusory singularity and integrity of the bounded self – a model that would thwart any move towards positive community – is contested in its very success. The transfer of bone marrow between siblings is at very least a step towards realising new potentials of becoming other than the separate and distinct self.

Research into the nature of microchimerism in organ and tissue transplantation – including bone marrow transplants and the projected use of stem cell transplants for neurological disorders – is driven by bioscience alone, but such procedures also constitute highly significant biopolitical objects. In effect, the biological ground that has reflected and sustained the biopolitical rhetoric of immunity, with its insistence on the distinct identities of self and other, is no longer viable. As both the postconventional humanities and bioscientific discourse increasingly acknowledge the plasticity of human embodiment, not simply in the context of established and future modifications of tissues or organs, but at the unseen cellular level, a new understanding of the inherent entanglement of corporeal materials is emerging. Multidisciplinary enquiry into transplantation suggests that rethinking the interweaving of chimerism and an immuno-politics could mobilise an ethical challenge to the damaging rigidities of the self/other model of modernity and insist instead on the fundamental diversity, mutability and connectivity of all corporeality. As it becomes increasingly clear that the incidence of chimerism and microchimerism is a ubiquitous facet of embodiment rather than a strange exception,Footnote 14 we should seek to find new models of thinking human life, not as a collection of time-bound individuals each defending the autonomous self, but through the fluid, interactive and communal dynamics of assemblage.