Use of T-cell growth factors (interleukins 2, 4, 7, 10, and 12) in the evaluation of T-cell reactivity to melanoma

Melanoma represents the single best example of a human tumor that has been shown to elicit specific T-cell reactivity. The responsiveness of some patients with metastatic melanoma to treatment with the prototypic T-cell growth factor (TCGF), interleukin-2 (IL-2), indicates that T cells play a role in antitumor immunity. Interleukin-4 (IL-4), another TCGF that has been administered clinically to humans, was not associated with tumor response in our trials conducted at the Surgery Branch of the National Cancer Institute. Combination trials of IL-2 with IL-4 have shown no increase in responsiveness of melanoma or other tumors when compared to IL-2 alone. However, enhanced expansion of tumor-infiltrating lymphocytes (TILs) in vitro has been observed with combinations of low-dose IL-2 and IL-4. We have begun a study evaluating the trafficking of such expanded lymphocytes following their adoptive transfer in association with systemic administration of IL-2 and IL-4. We have established several TIL cultures from fresh tumor samples, maintained them in long-term culture, and marked them with the neomycin phosphotransferase gene using the LNL6 retroviral vector. Such TILs appear to demonstrate no notable alterations in phenotype or cytolytic activity when compared to their nontransduced counterparts. In addition to IL-2 and IL-4, there are a variety of other novel TCGFs that are now available for evaluation in preclinical and clinical trials. IL-7 induces proliferation and lymphokine-activated killer (LAK) cell activity from human peripheral blood mononuclear cells. IL-7 also increases the proliferation of murine B and T cells located in the spleen and lymph nodes. Our studies of IL-7 reveal that expansion of TILs in combination with IL-2 is associated with the selective outgrowth of predominately CD4⁺ lymphocytes. IL-10 was originally defined as a factor inhibiting IL-2 and γ-interferon production by T-helper cells and thus termed cytokine synthesis inhibitory factor. Interestingly, murine IL-10 has been shown under certain circumstances to synergize with IL-2, IL-4, and IL-7 in the growth of thymic and peripheral T cells. A truncated version of IL-10 found within the Epstein- Barr virus genome (BCRF-2 or vIL-10) shares the cytokine synthesis inhibitory properties of IL-10 but does not appear to have TCGF activity. Interleukin-12 is a heterodimeric cytokine that enhances proliferation and cytolytic capacity of T cells and large granular lymphocytes. IL-12 synergizes with IL-2 in the induction of LAK cells, and induces the secretion of 7-interferon and tumor necrosis factor-α (TNF-α) from human peripheral blood mononuclear cells. IL-12 appears to be produced mainly by macrophages and B cells. Our initial studies demonstrate that IL-12 supports the growth of TILs previously cultured in IL-2. We have introduced both chains of the murine IL-12 gene into retroviral vectors and are beginning cytokine gene transfection studies. These studies will be combined with our ongoing evaluation of IL-2 and IL-4 transfection as a means to develop novel tumor vaccines.