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Cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) functions as a negative regulator of endogenous and vaccine-induced antitumor immunity. The administration of fully human anti-CTLA-4 blocking monoclonal antibodies to advanced-cancer patients increases immune-mediated tumor destruction in some subjects. Nonetheless, patients that respond also frequently manifest serious inflammatory pathologies, raising the possibility that the therapeutic and toxic effects of CTLA-4 blockade might be linked. Here we show that periodic infusions of anti-CTLA-4 antibodies after vaccination with irradiated, autologous tumor cells engineered to secrete GM-CSF (GVAX) generate clinically meaningful antitumor immunity without grade 3 or 4 toxicity in a majority of metastatic melanoma patients. The application of this sequential immunotherapy to advanced ovarian carcinoma patients also revealed that tumor destruction and severe inflammatory pathology could be dissociated, although further refinements are required to increase clinical responses and to minimize toxicity in this population. The extent of therapy-induced tumor necrosis was linearly related to the natural logarithm of the ratio of intratumoral CD8 + effector T cells to FoxP3 + regulatory T cells (Tregs) in posttreatment biopsies. Together, these findings help clarify the immunologic and clinical effects of CTLA-4 antibody blockade in previously vaccinated patients and raise the possibility that selective targeting of antitumor Tregs may constitute a complementary strategy for combination therapy.

A large number of cancer-associated gene products evoke immune recognition, but host reactions rarely impede disease progression. The weak immunogenicity of nascent tumors contributes to this failure in host defense. Therapeutic vaccines that enhance dendritic cell presentation of cancer antigens increase specific cellular and humoral responses, thereby effectuating tumor destruction in some cases. The attenuation of T cell activation by cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) further limits the potency of tumor immunity. In murine systems, the administration of antibodies that block CTLA-4 function inhibits the growth of moderately immunogenic tumors and, in combination with cancer vaccines, increases the rejection of poorly immunogenic tumors, albeit with a loss of tolerance to normal differentiation antigens. To gain a preliminary assessment of the biologic activity of antagonizing CTLA-4 function in humans, we infused a CTLA-4 blocking antibody (MDX-CTLA4) into nine previously immunized advanced cancer patients. MDX-CTLA4 stimulated extensive tumor necrosis with lymphocyte and granulocyte infiltrates in three of three metastatic melanoma patients and the reduction or stabilization of CA-125 levels in two of two metastatic ovarian carcinoma patients previously vaccinated with irradiated, autologous granulocyte–macrophage colony-stimulating factor-secreting tumor cells. MDX-CTLA4 did not elicit tumor necrosis in four of four metastatic melanoma patients previously immunized with defined melanosomal antigens. No serious toxicities directly attributable to the antibody were observed, although five of seven melanoma patients developed T cell reactivity to normal melanocytes. These findings suggest that CTLA-4 antibody blockade increases tumor immunity in some previously vaccinated cancer patients.