IMMUNOGENICITY OF GAMMA-IRRADIATED MYCOBACTERIUM TUBERCULOSIS H37RV (GIV) IN MICE.

Abstract

Results of experiments on a gamma -irradiated vaccine (GIV) are reported. Cells irradiated with 500,000 or 1,000,000 r were injected subcutaneously in mice. The tests for reproductive viability by culture and guinea pig inoculations indicated that 500,000 r was sufficient to inactivate the tubercle bacilli. No visible growth was observed in culture media inoculated with cells exposed to 500,000 or cells showed no gross signs of infection. A long-term vaccination study showed that the vaccinated mice became segregated into two nonoverlapping groups. One group consisted of animals which developed little or no immunity and died after challenge within the period Qf time during which all of the nonvaccinated controls died (15 to 28 days); in the other group, the mice developed sufficient immunity to live 2 to 6 times longer (55 to 191 days). In terms of survival rates on day 35 after challenge, vaccination with BCG or GIV, with or without adjuvant, protected a significant portion of the vaccinated population, as compared with the nonvaccinated controls, with the exception of a group of male mice vaccinated with 0.1 mg. of GIV with adjuvant and challenged with 0.75 mg of virulent tubercle bacilli. GIV with adjuvant protected significantly greater proportionsmore » of the mice than did the vaccine without adjuvant. BCG, protected a significantly greater proportion of the anlmals than 0.1 or 0.4 mg of GIV, with or without adjuvant, but the protection afforded by a single 1.6-mg dose or four doses of 0.1 mg of GIV with adjuvant was statistically equivalent to that of BCG, Cobalt-60-irradiated M. tuberculosis H37Rv, although unable to grow on culture media and to produce disease in lab animals, respires on suitable substrates. In acid-fast stained films the irradiated cells cannot be distinguished, morphologically or tinctorially, from the nonirradiated cells. Such gamma -irradiated cells, produced from a virulent pathogen, have the advantage of a living attenuated vaccine, i.e,, ability to metabolize, without its disadvantages, i.e., genetic differences from the virulent organism (such as with BCG) and the possibility of producing disease in susceptible animals (not a major problem with BCG vaccine). The major disadvantage of the BCG vaccine is its instability, since exposure to temperatures above 4 deg C for a few days or to light for a few hours or even a few minutes may affect its potency. Whether the same factors will adversely affect the gamma -irradiated vaccine has yet to be explored. (BBB)« less