Evan A. Farkash

B7 Costimulation Is Critical for Antibody Class Switching and CD8+ Cytotoxic T-Lymphocyte Generation in the Host Response to Vesicular Stomatitis Virus

ABSTRACT Antibody and cytotoxic T-lymphocyte (CTL) responses have critical roles in eliminating many viral infections. In addition to stimulation of the T-cell receptor, T cells require costimulatory signals to respond optimally. We evaluated the role of B7 costimulatory molecules (B7-1 and B7-2) in the immune response to viral infection using vesicular stomatitis virus (VSV) and mice lacking either B7-1 or B7-2 or both molecules. Mice lacking both B7-1 and B7-2 had essentially no anti-VSV immunoglobulin G1 (IgG1) response, decreased IgG2a responses, and normal IgM responses, while mice lacking either B7-1 or B7-2 had unaltered anti-VSV antibody responses compared to wild-type mice. Depletion of CD4+ cells further reduced the IgG2a response in mice lacking both B7 molecules, suggesting that CD4−cells may supply help for IgG2a in the absence of B7 costimulation. The absence of both B7 molecules profoundly reduced generation of both primary and secondary VSV-specific class I major histocompatibility complex (MHC)-restricted CTL, whereas VSV-specific CTL responses in mice lacking either B7-1 or B7-2 were similar to those of wild-type animals. Class I MHC-restricted CTL in wild-type mice were not dependent on CD4+ cells, suggesting that the failure of CTL in the absence of B7s is due to a lack of B7 costimulation directly to the CD8+ CTL. These data demonstrate that B7-1 and B7-2 have critical, overlapping functions in the antibody and CTL responses to this viral infection.

A patient death attributable to implant-related primary anaplastic large cell lymphoma of the breast.

Summary: Implant-related primary anaplastic large cell lymphoma (ALCL) of the breast is a rare clinical entity. With increasing attention being paid to this disease, most cases reported to date in the literature have demonstrated indolent clinical courses responsive to explantation, capsulectomy, chemotherapy, and/or radiotherapy. The authors describe a case of bilateral implant-related primary ALCL of the breast that proved refractory to both standard and aggressive interventions, ultimately resulting in patient death secondary to disease progression. The authors situate this case in the context of the current state of knowledge regarding implant-related primary ALCL of the breast and suggest that this entity is generally, but not universally, indolent in nature. CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, V.

Early Acceptance of Renal Allografts in Mice Is Dependent on Foxp3+ Cells

Mouse renal allografts have a remarkable ability to promote acceptance across full major histocompatibility complex incompatibilities in certain strain combinations without immunosuppression. The mechanism is unknown but is believed to involve immunoregulation. This study tests whether Foxp3(+) T-regulatory cells are responsible in the early phase of graft acceptance, using B6.Foxp3(DTR) mice that express diphtheria toxin receptor (DTR) in Foxp3(+) cells. The administration of DT to B6.Foxp3(DTR) recipients with accepted DBA/2 kidneys, 3 weeks to 3 months after transplantation, caused a marked depletion of Foxp3 cells and triggered acute cellular rejection, manifested by a sudden increase in blood urea nitrogen within a week. None of the controls showed an increase in blood urea nitrogen, including DT-treated B6 wild-type recipients of DBA/2 kidneys or B6.Foxp3(DTR) recipients of isografts. Accepted DBA/2 allografts showed prominent lymphoid sheaths around arteries containing numerous CD3(+)Foxp3(+) cells, CD4(+) cells, dedritic cells, and B cells, which was independent of CCR4. The lymphoid sheaths disintegrate after Foxp3 depletion, accompanied by widespread CD8 interstitial mononuclear inflammation, tubulitis, and endarteritis. The Foxp3 depletion caused an increased frequency of donor-reactive cells in the spleen by interferon (IFN) γ enzyme-linked immunosorbent spot (ELISPOT) assays and increased expression of the maturation markers, CD86 and IA(b), on dendritic cells in the spleen and kidney. We conclude that Foxp3(+) cells are needed to maintain acceptance of major histocompatibility complex-incompatible renal allografts in the first 3 months after transplantation and may act by inhibiting DC maturation.

Vascularized Composite Allograft Tolerance Across MHC Barriers in a Large Animal Model

Vascularized composite allograft (VCA) transplantation can restore form and function following severe craniofacial injuries, extremity amputations or massive tissue loss. The induction of transplant tolerance would eliminate the need for long‐term immunosuppression, realigning the risk–benefit ratio for these life‐enhancing procedures. Skin, a critical component of VCA, has consistently presented the most stringent challenge to transplant tolerance. Here, we demonstrate, in a clinically relevant miniature swine model, induction of immunologic tolerance of VCAs across MHC barriers by induction of stable hematopoietic mixed chimerism. Recipient conditioning consisted of T cell depletion with CD3‐immunotoxin, and 100 cGy total body irradiation prior to hematopoietic cell transplantation (HCT) and a 45‐day course of cyclosporine A. VCA transplantation was performed either simultaneously to induction of mixed chimerism or into established mixed chimeras 85–150 days later. Following withdrawal of immunosuppression both VCAs transplanted into stable chimeras (n = 4), and those transplanted at the time of HCT (n = 2) accepted all components, including skin, without evidence of rejection to the experimental end point 115–504 days posttransplant. These data demonstrate that tolerance across MHC mismatches can be induced in a clinically relevant VCA model, providing proof of concept for long‐term immunosuppression‐free survival.

Role of complement and NK cells in antibody mediated rejection.

Despite extensive research on T cells and potent immunosuppressive regimens that target cellular mediated rejection, few regimens have been proved to be effective on antibody-mediated rejection (AMR), particularly in the chronic setting. C4d deposition in the graft has been proved to be a useful marker for AMR; however, there is an imperfect association between C4d and AMR. While complement has been considered as the main player in acute AMR, the effector mechanisms in chronic AMR are still debated. Recent studies support the role of NK cells and direct effects of antibody on endothelium cells in a mechanism suggesting the presence of a complement-independent pathway. Here, we review the history, currently available systems and progress in experimental animal research. Although there are consistent findings from human and animal research, transposing the experimental results from rodent to human has been hampered by the differences in endothelial functions between species. We briefly describe the findings from patients and compare them with results from animals, to propose a combined perspective.

Rare lymphoid malignancies of the breast: a report of two cases illustrating potential diagnostic pitfalls

Breast involvement by lymphoma is uncommon and poses challenges in diagnosis. Lymphomas may clinically, radiologically, and morphologically mimic both benign and neoplastic conditions. We describe two cases of lymphoid malignancies predominantly involving the breast, both presenting diagnostic dilemmas. The first case, ALK-negative anaplastic large-cell lymphoma involving a seroma associated with a breast implant, is an emerging clinicopathologic entity. Anaplastic large-cell lymphoma has been identified in association with breast implants and seroma formation relatively recently. The second case, hairy cell leukemia involving the breast and ipsilateral axillary sentinel lymph node, is, to our knowledge, the first reported case of hairy cell leukemia involving the breast at the time of diagnosis. While a localized bone lesion was present at time of diagnosis, bone marrow involvement was relatively mild in comparison to that seen in the breast and lymph node. In the first case, lymphoma occurred in a clinical setting where malignancy was unsuspected, highlighting the importance of careful morphologic evaluation of paucicellular samples, as well as awareness of rare clinicopathologic entities, in avoiding a misdiagnosis of a benign inflammatory infiltrate. In the second case, the lymphoid neoplasm exhibited classic morphologic and immunophenotypic features, but presented at an unusual site of involvement. Knowledge of the patients concurrent diagnosis of hairy cell leukemia involving the bone marrow and bone helped avoid a misdiagnosis of carcinoma rather than lymphoma.

Diagnostic challenges in chronic antibody-mediated rejection.

Measurement of glomerular and peritubular capillaritis in kidney transplant biopsy samples identifies allograft dysfunction associated with alloantibodies. Sis et al. show that this technique has a higher sensitivity but lower specificity than the current diagnostic criteria using peritubular capillary C4d deposition, and that capillaritis is an independent predictor of progression to graft failure.

Pathology: Diagnostic challenges in chronic antibody-mediated rejection

Measurement of glomerular and peritubular capillaritis in kidney transplant biopsy samples identifies allograft dysfunction associated with alloantibodies. Sis et al. show that this technique has a higher sensitivity but lower specificity than the current diagnostic criteria using peritubular capillary C4d deposition, and that capillaritis is an independent predictor of progression to graft failure.

Either B7 Costimulation or IL-2 Can Elicit Generation of Primary Alloreactive CTL

B7-1 and B7-2 are important costimulatory molecules in the activation of T cell immunity. We have used mice made genetically deficient in either or both B7 molecules to determine the role of B7 molecules in activation of primary alloreactive CTL. The absence of either B7-1 or B7-2 did not alter generation of CTL from unfractionated lymphocytes, but the absence of B7-2 greatly decreased CTL generation from purified CD8+ responder cells. However, if B7-1 was induced on the stimulating cells then CTL generation was restored to wild-type levels. Absence of both B7-1 and B7-2 from MLR using whole splenocytes resulted in a profound reduction in generation of CTL. This could completely be reversed by the addition of IL-2. B7 molecules could directly costimulate CD8+ cells, as purified CD8+ cells developed into mature CTL when stimulated with wild-type APC, but not with B7-deficient APC. Again, IL-2 could drive CTL generation from purified CD8+ cells, even in the absence of B7 molecules. Taken together, these results demonstrate an important role for B7 costimulation in CTL generation.

Prolonged Survival of Pig Skin on Baboons After Administration of Pig Cells Expressing Human CD47.

BackgroundSuccessful xenotransplantation will likely depend, in part, on the induction of immunological tolerance, because the high levels of immunosuppression otherwise required would likely have unacceptable side effects. Rapid clearance of administered porcine hematopoietic stem cells by primate macrophages has hampered previous attempts to induce tolerance through mixed hematopoietic chimerism across a pig-to-primate barrier. Phagocytosis is normally inhibited by binding of cell surface protein CD47 to macrophage signal regulatory protein &agr; receptors. However, pig CD47 has previously been shown to be ineffective in transducing signals through primate signal regulatory protein &agr;. MethodsMobilized peripheral blood hematopoietic cells from transgenic swine expressing high or low levels of human CD47 were infused into conditioned baboons at 3 time points over a 9-week period. Xenogeneic peripheral blood chimerism was assessed after each infusion. Split thickness skin grafts from the hematopoietic cell donor swine were placed on recipients 5 weeks after the last cell infusion and 7 weeks after the discontinuation of all immunosuppression to test immune response. ResultsThe level and duration of transient chimerism were substantially greater in baboons receiving hematopoietic cells from a pig expressing high levels of human CD47. Skin graft survival on high CD47 recipients was prolonged as well, in 1 case showing no signs of rejection at least 53 days after placement. ConclusionsProlongation of transient porcine chimerism via transgenic expression of human CD47 in a primate model is associated with an immune modulating effect, leading to markedly prolonged survival of donor swine skin xenografts that may be applicable to clinical solid organ xenotransplantation.