Differential promotion of hematopoietic chimerism and inhibition of alloreactive T cell proliferation by combinations of anti-CD40Ligand, anti-LFA-1, everolimus, and deoxyspergualin

Signal one and two blockade are both critical for non-myeloablative murine HSCT across a major histocompatibility complex barrier

Non-myeloablative allogeneic haematopoietic stem cell transplantation (HSCT) is rarely achievable clinically, except where donor cells have selective advantages. Murine non-myeloablative conditioning regimens have limited clinical success, partly through use of clinically unachievable cell doses or strain combinations permitting allograft acceptance using immunosuppression alone. We found that reducing busulfan conditioning in murine syngeneic HSCT, increases bone marrow (BM):blood SDF-1 ratio and total donor cells homing to BM, but reduces the proportion of donor cells engrafting. Despite this, syngeneic engraftment is achievable with non-myeloablative busulfan (25 mg/kg) and higher cell doses induce increased chimerism. Therefore we investigated regimens promoting initial donor cell engraftment in the major histocompatibility complex barrier mismatched CBA to C57BL/6 allo-transplant model. This requires full myeloablation and immunosuppression with non-depleting anti-CD4/CD8 blocking antibodies to achieve engraftment of low cell doses, and rejects with reduced intensity conditioning (≤75 mg/kg busulfan). We compared increased antibody treatment, G-CSF, niche disruption and high cell dose, using reduced intensity busulfan and CD4/8 blockade in this model. Most treatments increased initial donor engraftment, but only addition of co-stimulatory blockade permitted long-term engraftment with reduced intensity or non-myeloablative conditioning, suggesting that signal 1 and 2 T-cell blockade is more important than early BM niche engraftment for transplant success.

Inhibition of recall responses through complementary therapies targeting CD8+ T-cell- and alloantibody-dependent allocytotoxicity in sensitized transplant recipients

Allospecific T memory cell responses in transplant recipients arise from environmental exposure to previous transplantation or cross-reactive heterologous immunity. Unfortunately, these memory responses pose a significant barrier to the survival of transplanted tissue. We have previously reported that concurrent inhibition of CD154 and LFA-1 suppresses primary CD8-dependent rejection responses that are not controlled by conventional immunosuppressive strategies. We hypothesized that CD154- and LFA-1-mediated inhibition, by targeting activation as well as effector functions, may also be efficacious for the control of alloreactive CD8+ T-cell responses in sensitized hosts. We found that treatment with anti-LFA-1 mAb alone enhanced transplant survival and reduced CD8-mediated cytotoxicity in sensitized CD4 KO recipients. However, treatment with anti-CD154 mAb alone did not have an effect. Notably, when both CD4- and CD8-dependent rejection pathways are operative (wild-type sensitized recipients), LFA-1 significantly inhibited CD8-mediated in vivo allocytotoxicity but did not correspond with enhanced hepatocyte survival. We hypothesized that this was due to alloantibody-mediated rejection. When anti-LFA-1 mAb treatment was combined with macrophage depletion, which we have previously reported impairs alloantibody-mediated parenchymal cell damage, in vivo cytotoxic effector function was significantly decreased and was accompanied by significant enhancement of hepatocyte survival in sensitized wild-type recipients. Therefore, LFA-1 is a potent therapeutic target for reduction of CD8-mediated cytotoxicity in sensitized transplant recipients and can be combined with other treatments that target non-CD8-mediated recall alloimmunity.

Rapamycin as immunosuppressant in murine transplantation model

The potent immunosuppressive action of rapamycin has been described in many different mouse models of transplantation. In these models, rapamycin prevent or delay allograft rejection. In several models, rapamycin allowed mixed donor-recipient hematopoietic chimerism to develop facilitating tolerance induction. In our own experience, we observed that rapamycin synergized with CD8(+) T cell depletion and coreceptor/costimulation blockade to induce long-term survival of Balb/C to C57Bl/6 heterotopic limb allograft. Herein, we describe immunosuppression cocktails containing rapamycin and methods to evaluate several read outs associated with tolerance induction such as mixed donor-recipient hematopoietic chimerism and in vitro or in vivo recipient alloreactivity.

Update on vaccine development for renal cell cancer

Renal cell carcinoma (RCC) remains a significant health concern that frequently presents as metastatic disease at the time of initial diagnosis. Current first-line therapeutics for the advanced-stage RCC include antiangiogenic drugs that have yielded high rates of objective clinical response; however, these tend to be transient in nature, with many patients becoming refractory to chronic treatment with these agents. Adjuvant immunotherapies remain viable candidates to sustain disease-free and overall patient survival. In particular, vaccines designed to optimize the activation, maintenance, and recruitment of specific immunity within or into the tumor site continue to evolve. Based on the integration of increasingly refined immunomonitoring systems in both translational models and clinical trials, allowing for the improved understanding of treatment mechanism(s) of action, further refined (combinational) vaccine protocols are currently being developed and evaluated. This review provides a brief history of RCC vaccine development, discusses the successes and limitations in such approaches, and provides a rationale for developing combinational vaccine approaches that may provide improved clinical benefits to patients with RCC.