Biological Activity of the Suppressor Cells Inducer Factor Secreted by the Jeg‐3 Choriocarcinoma Cell Line

PROBLEM: We wanted to further study the mechanisms of immune suppression and suppression inducing capacities by choriocarcinoma products, e.g. both crude human choriocarcinoma supernatant (HCS) and especially an active fraction obtained by high performance liquid chromatography (HPLC) from the culture supernatant of the Jeg‐3 human choriocarcinoma cell line, since it appeared by weight and charge criteria to be a different molecular species than the low molecular weight fraction previously isolated from mouse and human term placenta. It was important to know whether the purified material was active in vivo as it was in vitro. Therefore, we tested the effects of HCS in vivo in three systems: prevention of fetal demise in the CBA/J×DBA/2 abortion prone murine mating combination, where the effects of the HPLC purified fraction were also monitored as well as by a cell transfer system, where the suppression is revealed by a local GVH/HVG assay, and finally enhancement the survival of a mildly immunogenic tumor allograft.
 METHODS: An active fraction was isolated from HCS by ion exchange HPLC. Female CBA/J were mated with DBA/2 and the influence of 3 intraperitoneal injections of both crude HCS and the active fraction was evaluated by monitoring the percentage of fetal resorptions. Simultaneously, on the day when resorptions were counted, maternal splenocytes from these females were harvested and were injected by the subcutaneous way in C3H/HEJ hind feet. The lymph node reactivity (HVG+GVH) was assessed by [3H]thymidine intake by cells harvested from the draining popliteal lymph nodes. For assessment of influence of HCS on allograft rejection, BALB/b (H‐2b) mice received a subcutaneous injection of allogeneic P815 tumor cells (H‐2d). The influence of HCS injections on tumor survival was analyzed by regular measurements of the mean tumor diameter.
 RESULTS: Intraperitoneal injection of HCS reduced fetal resorptions from 24.7 to 13%. Injection of the in vitro active fraction induced the same rate of reduction. The mean intensity of HvG/GvH reaction was 13 400 cpm per lymph node when splenocytes from the control group were injected compared to 2900 cpm when splenocytes from treated mice were used. P815 tumor allografts were completely rejected in all cases after 21 days. Weekly subcutaneous injections of HCS prolonged tumor survival in all cases up to at least 30 days.
 CONCLUSION: The fraction isolated from HCS increased very efficiently the survival of allografts as well as those of allogeneic fetuses in a resorption prone murine mating. The choriocarcinoma cell line might prove to be a useful source of immunosuppressive materials, which could otherwise be important for the fetal–maternal tolerance and a successful pregnancy.