PT-9K/129G, a nontoxic mutant of pertussis toxin (PT) obtained by genetic manipulation, has been shown in animal models to be a promising candidate for new vaccines against whooping cough. To assess the safety and the immunogenicity of PT-9K/129G in humans, a pilot study has been performed in adult volunteers. The protein was found to be safe, capable of inducing high titers of toxin-neutralizing antibodies, and capable of generating immunological memory. In fact, vaccination caused an increase of cell-mediated response to PT, PT-9K/129G, S1 subunit, and B oligomer, indicating that memory T cells are induced by the vaccine. Since PT-9K/129G is mitogenic for T lymphocytes in vitro, it was investigated whether this activity is also present in vivo. No variation was observed in the proportion of T cells (CD3+), T helper cells (CD4+), and cytotoxic T cells (CD8+), as well as in that of other lymphoid populations, by FACS analysis. Interestingly, no thorough correlation was found between humoral and cellular responses. In one case, a very high cellular response was present in absence of detectable antibodies, suggesting that the antibody response, which is the only parameter measured in most clinical trials, may not give a complete picture of the response induced by a vaccine.
Metabolic, humoral and cellular responses in adult volunteers immunized with the genetically inactivated pertussis toxin mutant PT-9K/129G / Podda, A.; Nencioni, L.; DE MAGISTRIS, M. T.; DI TOMMASO, A.; Bossu', P.; Nuti, S.; Pileri, P.; Peppoloni, Samuele; Bugnoli, M.; Ruggiero, P.; Marsili, I.; Derrico, A.; Tagliabue, A. AND RAPPUOLI R.. - In: JOURNAL OF EXPERIMENTAL MEDICINE. - ISSN 0022-1007. - STAMPA. - 172:(1990), pp. 861-868.