La Pedagogía como reflexión y ciencia de la educación

1.8.1 Autologous BMT

70% of patients with AML do not have a matched sibling donor and therefore are reliant on chemotherapy alone, a matched unrelated donor or an autologous transplant for a cure (Talbot et a/., 1990). In autologous transplantation the bone marrow is taken from the patient and then they undergo high dose chemotherapy and radiotherapy before the re-infusion of their previously stored bone marrow. The procedure is much less toxic than the conditioning required for an allogeneic transplant. The patient does not receive any cells that would be seen as foreign; the conditioning regimen is therefore less severe and can be performed on older patients. It also has the advantage of readily available material for grafts, and no inherent risks of GvHD.

1.8.2 ‘Autologous GvHD‘ induced by cyclosporin

The anti-leukaemic effect of autologous grafts is presumably less than that of allogeneic transplants, because these grafts are lacking the immunogenic stimulus provided by alloantigens. Given the association between GvL and GvHD, some groups have tried to break immune tolerance to self-antigens in order to provoke ‘autologous GvHD’.

It has been shown that an acute GvHD-like condition could be induced by cyclosporin in AML patients who had received autologous BMT, but the results in terms of disease-free survival have been disappointing (Talbot et al., 1990). In rat studies the administration of cyclosporin resulted in auto-cytotoxic T cells which recognised self class II MHC antigens, and showed a reduction in T helper cells (Hess et al., 1985). In a small patient study auto-GvHD was induced in 50% of recipients, but they subsequently suffered a prolonged period of aplasia (Garin et al., 1996). This route of research although potentially very exciting has not proved as fruitful as at first hoped.

1.8.3 The use of LAK therapy

Lymphokine activated killer (LAK) cells are mainly MHC non-restricted and are defined as cells which are capable of killing NK-resistant targets after incubation with IL-2. In a study of patients with CML, LAK cells were generated by incubating peripheral blood mononuclear cells with recombinant IL-2 for up to seven days (Mackinnon et al., 1990). The predominant phenotype of these cells was CD56^/CD8VCD4' with a variable number of cells co-expressing CD3 [and hence termed NKT cells]. LAK cells were able to inhibit CML colony

forming units-granuiocyte-macrophage (CFU-GM) proliferation, but did not inhibit donor marrow CFU-GM to the same degree, which suggests a GvL effect. Although the LAK population did include NKT cells, killing of recipient CML cells was maintained in this study even after depletion of CD3^ cells (Mackinnon etal., 1990).

This work demonstrated a role for LAK cells in vitro, and diminished the importance of the CD3^ T cell. From this stemmed the idea that the GvL effect could be enhanced by the use of IL-2, without incurring GvHD. The trials that ensued covered the use of IL-2 in vivo with or without BMT, the use of IL-2 in

vitro to stimulate NK/LAK responses and the subsequent infusion of activated

cells, and the combination of in vivo IL-2 with NK/LAK cell therapy. This treatment was particularly popular with autologous BMT due to the higher relapse rate as compared with allogeneic BMT, and indeed a study from this centre showed that it could reduce the relapse risk from 54% to 17% (Hamon et ai., 1993).

The trials varied the administration of IL-2 by continuous intravenous infusion or bolus infusion (Higuchi et ai., 1991, Soiffer et ai., 1992) also the length and the timing of the treatment was altered. Initially the treatment seemed to be well tolerated and in all cases resulted in an increased number of CD56%D 16^/CD3" cells. However, problems resulted because early treatment post-autologous BMT with an IL-2 infusion was required to prevent relapse. Although IL-2 is followed by rebound lymphocytosis which is valuable in the

thrombocytopenia, also administration of IL-2 itself results in thrombocytopenia which is not desirable early after allogeneic BMT (Benyunes et al., 1993).

In a larger study conducted by Hauch et al the primary effector cells post transplant against host-derived and fully allogeneic CML targets were found to be CD56^/CD 16VCDS', these cells had been cultured in medium containing IL-2 (Hauch et a/., 1990). Also in this study those patients who failed to generate lytic activity against host CML cells were much more likely to relapse (72%) when compared with those whose LAK cells did lyse host CML cells (7%, p=0.002).

The best results achieved with LAK cell therapy have been reported from the Seattle group (Benyunes et a/., 1993). In 14 patients with AML in relapse or CR 2 the administration of IL-2 +/- LAK cells after ABMT gave a 4 year survival probability of 71%, suggesting that the benefit of IL-2 therapy may require the presence of minimal residual disease to generate a leukaemia-specific immune response.

NK cells have the advantage over T cells in that they do not require priming and they are MHC non-restricted. It appears however that the activation by IL-2 in

vivo or in vitro is crucial to maximise the NK cell's potential and without that their ability to lyse leukaemic targets is limited. However, despite the obvious benefits of IL-2 as a means of stimulating cells the side effects have made effective therapy difficult. The number of clinical studies therefore has reduced dramatically since the early 1990s, due to treatment toxicity and the

thrombocytopenia frequently seen early on after BMT which negates the effect of an IL-2 infusion. It is possible though that another cytokine which shares the ability possessed by IL-2 to activate cells, could be used in its place if found to be less toxic. One candidate for this role is IL-15 which is central to this study.

This project was designed to give a comprehensive overview of immune reconstitution, after T-cell depleted and non-depleted allogeneic and autologous grafts. This was done in an attempt to uncover the likely effector cells in allogeneic GvL, and to compare the role of these cells in autologous transplant recipients and patients treated with chemotherapy alone. Autologous leukaemia reactive cytotoxic cells were identified and culture conditions investigated for in vitro maintenance and proliferation by using combinations of cytokines.

2. Immune reconstitution after bone marrow