T-cells inhibit Friend murine leukemia virus infection of B-cells in vitro

The effect of immunization with killed tumor cells, with/without feeding of Echinacea purpurea in an erythroleukemic mouse model

OBJECTIVE

Tumor amelioration via vaccination/immunization is a practice for which considerable experimental and clinical support is growing. Combination therapies have proven to be more beneficial than treatment with single agents. We hypothesized that immunization of mice with killed erythroleukemia cells prior to the induction of erythroleukemia via injection of viable tumor cells, plus dietary administration of a known immuno-enhancing phytocompound, Echinacea purpurea, would be more effective than immunization alone.

DESIGN

A commercially available extract of E. purpurea root, already proven as a natural killer (NK) cell stimulant, was administered via the chow, for periods of 9 days or 3 months after the onset of leukemia to mice which had been injected (immunized) 5 weeks earlier with killed leukemia cells.

RESULTS

Immunized mice (+/- E. purpurea) had significantly prolonged life spans versus non-immunized mice, with an even greater proportion of hosts surviving long-term in the E. purpurea-fed group. NK cells, the mediators of nonspecific immunity and well-demonstrated mediators of tumor cytolysis, were very significantly elevated in immunized, leukemic mice receiving E. purpurea in their diet versus those receiving untreated chow. Early in tumor development (9 days), cells mediating specific immunity (T, B lymphocytes) were 10-12 times higher in absolute numbers in the spleens in all immunized, leukemic mice vs unimmunized, leukemic mice at the same stage of tumor progression.

CONCLUSIONS

The results demonstrate that combination therapy, involving specific tumor cell immunization, followed by daily phytotherapy (dietary E. purpurea), sensitized the immune cells and led to life span prolongation greater than that provided by immunization alone.

Induction of permanent regression of Friend virus (FV) leukemia by adoptive transfer of T helper and not T cytotoxic cells

Friend virus (FV) induces a progressive erythroleukemia that can be made to permanently regress by the transfer of in vitro cultured virus-specific T cells (CTL/RFB) without any other adjunctive treatment. To determine the role of T cells in regression, CTL/RFB were enriched for specific T-cell subsets by treatment with monoclonal anti-Lyt2.2 or anti-L3T4 antibody and complement (C'). Pre-treatment of CTL/RFB with anti-Lyt2 antibody and C' did not affect permanent regression incidence, while CTL/RFB depleted of L3T4+ cells induced temporary regressions with all mice recurring. The number of splenic Lyt2+ (CD8+ equivalent) cells was constant irrespective of the leukemic status of the animals. However, the number of L3T4+ cells (CD4+ equivalent) in leukemic mice was three-fold lower than that of normal mice with regressed mice demonstrating a 30% increase in the number of L3T4+ cells compared to normals. Spleen cells from leukemic animals were also unable to produce IL-2 in response to mitogen stimulation. These results indicate that L3T4+ cells are involved in regression of erythroleukemia.