Simulataneous Vaccination and Delayed Lymphocyte Infusion for Enhancement of Immune Reactivity Against Acute Lymphoblastic Leukemia or Lymphoma.

BACKGROUND: Delayed lymphocyte infusion (DLI) can be employed as an antileukemia immune therapy when patients with leukemia relapse after allogeneic hematopoietic stem cell transplantation (HSCT). While effective in patients with chronic myelogenous leukemia, it is generally ineffective with relapse of acute lymphoblastic leukemia (ALL). This ineffectiveness may be multifactorial and possible reasons include rapid leukemia cell growth in ALL, reduced propensity to apoptosis signals, and poor presentation of antigens present on lymphoblasts resulting in failure to generate a significant immune response. If the failure of malignant lymphoblasts in marrow and lymphoid tissues to elicit meaningful T cell responses plays a role in the ineffectiveness of DLI, it is possible that therapeutic vaccines may be able to ameliorate this barrier. We have recently demonstrated that vaccination immediately prior to HSCT enhances antigen specific T cell responses in the post-transplant immune repertoire (Bone Marrow Transplantation, 35:793–801, 2005.)

HYPOTHESIS: Vaccination with leukemia related antigens at the time of DLI will increase donor T cell responses to leukemia related antigens without exacerbation of GVHD responses to ubiquitous host minor histocompatibility antigens (mHA).

METHODS: We employ a murine MHC matched allogeneic HSCT model in which 6 antigens are molecularly characterized. C3.SW mice are donors and C57BL/6 mice are recipients. In this model the H7 mHA is the immunodominant antigen, while alloresponses to H3 and H13 are also present. By using spontaneously arising lymphoblastic leukemia/lymphoma cells from Ig-cmyc transgenic male C57BL/6 as the model malignancy in a female to female transplant the male HY associated antigens Uty, Dby and Smcy can be used as antigens restricted to the lymphoid malignancy. Four weeks after allogeneic HSCT mice were vaccinated with 10⁷ cells expressing the HY antigens and the C57BL/6 H7, H3 and H13 minor antigens. The cells used for pre-DLI vaccination were either irradiated male C57BL/6 spleen cells or irradiated male malignant lymphoblasts. One day later mice received iv infusion of 10⁷ spleen cells from C3.SW female donor mice previously primed against HY antigens by immunization with male C3.SW cells. Ten days interferon gamma Elispot assays were performed on HSCT recipient spleen cells using the peptide-defined antigens.

RESULTS: Vaccination of HSCT recipients with male spleen cells 1 day prior to DLI from HY immune donors significantly increased T cell responses to HY peptide epitopes. Recipients of DLI alone harbored 40 interferon secreting cells per 10⁶, while combination of vaccination and DLI yielded 94 per 10⁶(p < 0.05). In contrast, there was no change in the number of T cells responding to the H7, H3 and H13 mHA. DLI only exhibited 26 per 10⁶ while DLI plus vaccine exhibited 27 per 10⁶ (p < 0.05). Whole cell irradiated lymphoblasts were not as effective as irradiated splenocytes in augmenting the HY responses, although they were equally effective in producing T cell responses in normal, nontransplanted mice.

CONCLUSIONS: Simultaneous vaccination and DLI can lead to significant expansion of donor cells potentially reactive with antigens present on malignant lymphoblasts without exacerbation of T cell responses to ubiquitous mHA associated with GVHD. Current work is exploring methods by which indirect presentation of antigens from lymphoblasts can be enhanced, since it is unlikely that vaccines relying on direct antigen presentation by lymphoblasts will be effective.