Anti-idiotypic antibody used for the localization of parenterally administered monoclonal anti-progesterone antibody in mice

Proto-oncogene erbA expression and increased abundance of progesterone receptors in the mouse uterus after passive immunisation against progesterone before implantation

Passive immunisation with a monoclonal anti-progesterone antibody (DB3) prevents pregnancy in the mouse, and antibody is localised in the endometrium before the onset of implantation. BALB/c female mice were injected intraperitoneally with 9 nmol of DB3 (a dose known to cause 100% infertility) 32 h post coitum, and the uterus was removed at various times after injection. Using a monoclonal anti-progesterone receptor antibody (PR6), expression of progesterone receptors was found to be abundant in uterine tissue of DB3-treated mice; this was associated with substantial progesterone receptor mRNA levels and with maximum localisation of DB3 antibody as detected by anti-idiotype antibody. Control animals treated with an equal amount of the mouse myeloma protein P3 showed very low levels of progesterone receptor in the uterus. DB3 treatment also affected uterine expression of the proto-oncogene erbA product (which shows primary sequence homology with the progesterone receptor) as revealed by specific antiserum to the ERBA protein and by in situ hybridisation with a cDNA probe to v-erbA. Time-course studies indicated that the erbA gene was expressed at a high level before progesterone receptor expression increased, that its expression was dependent on the presence of the embryo and that erbA expression persisted longer in DB3-treated females. The observations suggest that anti-progesterone immunisation has a direct effect within the uterus, involving persistence of proto-oncogene erbA expression (which itself may represent an early maternal response to pregnancy) and increased progesterone receptor levels resulting from an unopposed oestrogen effect derived from local ligand withdrawal.

Biotinylated anti-progesterone monoclonal antibodies specifically target the uterine epithelium and block implantation in the mouse

Post-coital administration of a mouse monoclonal antibody (mAb) against progesterone (DB3; IgG1) prevents pregnancy in several species. Our previous studies in mice have shown that passively transferred DB3 specifically targets the uterus before the expected time of implantation, probably through progesterone-binding sites. DB3 and two other anti-progesterone mAbs, i.e. 11/34 (IgG1) and 11/64 (IgM), were biotinylated and 9 nmol of each (a dose known to reduce pregnancy rate by greater than 80% with unconjugated mAbs) was injected into BALB/c female mice 32 h post coitum (p.c.). The biotin-mAb complexes were highly effective in blocking pregnancy (83-100%) compared with control animals that had received the biotinylated MOPC21 myeloma protein P3 (IgG1). Using the streptavidin-FITC (fluorescein isothiocyanate) reporter complex or second-stage anti-biotin-FITC antibodies, biotinylated conjugates of DB3, 11/34 and 11/64 were specifically localized on the uterine luminal epithelium at 68 h p.c. (i.e. 36 h after i.p. injection). Neither P3-biotin-treated pregnant mice nor biotinylated anti-progesterone mAb-treated pseudopregnant females showed a positive reaction. In addition, the localization of biotin-conjugated anti-progesterone mAbs could be blocked by absorption of the antibodies with free progesterone or progesterone conjugates prior to injection. These results show that localization to the uterine epithelium occurs with different anti-progesterone mAbs, and that this phenomenon is probably associated with progesterone-binding sites on the luminal epithelium.

Blocking of pregnancy in mice by immunization with anti-idiotype directed against monoclonal anti-progesterone antibody

Passive transfer of monoclonal anti-progesterone antibodies shortly after mating blocks the onset of pregnancy in different species (mouse, rat, and ferret). Here we report that BALB/c mice can be actively immunized against progesterone, and hence against pregnancy, by means of rabbit anti-idiotypic antibodies specific for a mouse monoclonal anti-progesterone antibody, DB3. Some of the anti-idiotypic antibodies reacted with the steroid-combining site on the DB3 molecule. In response to repeated anti-idiotypic immunization, mice produced serum anti-progesterone antibodies (up to 100 micrograms/ml) that resembled DB3 in idiotypy, affinity, and specificity for progesterone and other steroid ligands. Thus an anti-idiotype can mimic the antigenicity of a steroid hormone with a high degree of accuracy. Compared with immunization with a progesterone-bovine serum albumin conjugate, the anti-progesterone response to anti-idiotype was considerably lower and clonally restricted. When mated after completion of the immunization course, the fertility rate of anti-idiotype-immunized mice was reduced to 30% from a control level of 91%. The anti-fertility effect was correlated with the circulating anti-progesterone concentration in individual animals and persisted for 4 or 5 estrous cycles. Active immunization with progesterone-bovine serum albumin was a highly effective means of rendering mice infertile; it reduced the fertility rate to zero over 16 or 17 estrous cycles. Our results suggest that anti-idiotypes may form the basis of contraceptive vaccines.