Comparative Immunogenicity of Various Cellular and Cell-Free Preparations in a Leukemia Isotransplant System

Summary

Cells from established cultures of mouse cells (line D) infected with a murine lympheleukemesenle virus (B/T-L) were effective in immunization of mice against isotransplantation of leukemias induced by that virus. The immunogenicity of these cells was reduced from 96–100% to 43–51% as a result of unprotected freeze-thaw or homogenization procedures, these treatments also caused marked loss of cell viability and integrity, though the leukemogenic potential of the virus present was not significantly affected. Light irradiation (15 krads ⁶⁰Co) of cell suspensions halted cell multiplication, but did not impair their immunogenicity, temporary maintenance in vitro, or trypan blue viabilitYi the leukemogenic potential of the B/T-L virus was also unimpaired by this dosage. Heavy irradiation (500 krads ⁶⁰Co), on the other hand, reduced the immunogenicity of the cell suspensions from 96% to 23% and cell maintenance in vitro to Oi at this dose of irradiation, the immunogenic and leukemogenic activities of the virus suspensions were completely destroyed, dropping from 90% and 100%, respectively, to 0. The following procedure was therefore chosen for preparation of optimally immunogenic, nonmultiplying, and storable cellular vaccines in this system: suspension of viable cells in an isotonic solution of glucose, KCI, and NaCI to a density of 3–5 million/ml, light irradiation at 15 krads 60Co, addition of serum to 2% and glycerin to 5–8%, and slow freezing at −60°C. Just before use, a preparation should be thawed in a 37°C water bath, with constant agitation of the suspension during thawing. The trypan blue viability of such cells was consistently 75–95% before and after freezing; immunogenicity was 90–100%. The data suggest that intact cell membrane and viable virus contribute about equally to cellular immunogenicity in this system, and the implications are discussed.