PTPRC and neoplasm: Having established by immunohistochemistry the presence of human CD45+ leukocytes CD3+ T cells, CD20+ B cells and CD138+ plasma cells in the tumor microenvironment of xenografts established following the i.p. injection of tumor-derived cell aggregates (Fig. 3B), the viability and the capacity of these cells to respond to exogenous cytokine stimulation in vivo were investigated.