Human monoclonal antibody stability and activity at vaginal pH

Philip E. Castle, Daniel A. Karp, Larry Zeitlin, E. Bertrand García-Moreno, Thomas R. Moench, Kevin J. Whaley, Richard A. Cone

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


Antibodies can be delivered topically to the vagina to protect against pregnancy and sexually transmitted infections, but the acidity of vaginal secretions (pH 3.5-4.5) might inactivate them. To address this question, both experimental and computational methods were used to evaluate the effects of pH on human monoclonal antibody (MAb) stability and activity. To determine the acid-sensitivity of their antigen binding sites, human MAbs against human sperm (H6-3C4) and gp120 of HIV (1511) were tested by ELISA for binding to human sperm and recombinant gp120, respectively, at pH 3.0-7.0, after storing them for 1 or 20 h at the same pH. Binding was unaltered by acidic pH≥4 even after 20 h, and at pH 3.5 both MAbs retained ≥40% antigen binding activity. A humanized MAb against HSV-2 glycoprotein B expressed both in Chinese hamster ovary (CHO) cells and in soybean cells was incubated for 1 or 24 h at pH 3.5-7.6, brought to neutral pH, and tested for ability to block HSV-2 infection of foreskin fibroblast cells. Loss in blocking activity occurred only when antibodies were incubated at pH 3.5 for 24 h and was independent of the expression cell type. Using empirical structure-based methods, net charge, Z, and electrostatic contributions to free energy, ΔΔGel, were calculated as a function of pH for 1 human and 8 murine F(ab)s. The calculations indicate that Z changes slowly between pH 5.0 and 9.0 and that ΔΔGel is nearly constant between pH 4.0 and 10 for all the F(ab)s and, therefore, human antibodies should remain stable in this pH range. Taken together, our data and empirical calculations suggest that vaginally applied human MAbs are likely to remain stable and active throughout the duration they are likely to reside in the vagina.

Original languageEnglish (US)
Pages (from-to)61-76
Number of pages16
JournalJournal of Reproductive Immunology
Issue number1-2
StatePublished - 2002
Externally publishedYes


  • HIV
  • HSV
  • Monoclonal antibodies
  • Plantibodies
  • Sperm
  • Vagina

ASJC Scopus subject areas

  • Immunology and Allergy
  • Immunology
  • Reproductive Medicine
  • Obstetrics and Gynecology


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