Cyclophosphamide preconditioning facilitates autoimmune vitiligo and enhanced antitumor efficacy following vaccination with activated dendritic cells.

Abstract

Abstract Cyclophosphamide (CTX) has been used as a lymphoablative conditioning agent to deplete regulatory T cells (Tregs) and enhance the efficacy of adoptive immune therapies. We initially investigated whether CTX conditioning could enhance the immunogenicity of melanoma Ag-pulsed dendritic cells (DC) in a murine model. CTX enhanced Ag-specific CD8+ T cell responses and control of SC-growing OVA+ melanoma following immunization with activated OVA257–265-pulsed DC; immunogenicity and tumor control were abrogated by reconstitution of Treg compartments. Unexpectedly, CTX-conditioned, DC-immunized animals developed significant vitiligo, despite the absence of exogenous melanocyte-specific Ag in the vaccine. CTX treatment or DC immunization alone failed to induce vitiligo. Injection of CTX-conditioned mice with MHC class II−/− DC, but not β2 microglobulin−/− DC, induced vitiligo regardless of exogenous Ag, suggesting that the induction of vitiligo may result from cross-presentation of endogenous melanocyte Ag in an environment of relaxed tolerance. Ab-mediated depletion of CD8 cells abrogated the vitiligo. These data suggest that CTX conditioning liberates class I-restricted melanocyte Ag for cross-presentation by activated DC to cognate CD8 cells, which in turn, achieve full activation and effector function in the absence of a normal regulatory environment. CTX conditioning may also open dermal compartments for increased effector T cell infiltration. Thus, CTX mediates multiple immunomodulatory mechanisms that may impact the future design of immunotherapy for melanoma.