Development of a whole killed feline leukemia virus vaccine.

A whole killed FeLV vaccine was developed. By use of a chromatography method of purification and concentration, the resulting vaccine has been shown to be significantly lower in bovine serum albumin and total protein contents than were the same ingredients in the starting materials. The virus was inactivated or killed as an essential part of the vaccine development process. Vaccination trials with the vaccine without use of adjuvants indicated appreciable virus-neutralizing serum titer (greater than or equal to 1:10) in 107 of 110 vaccinated cats. Of 43 cats vaccinated and subsequently challenge exposed with virulent FeLV, only 2 developed persistent virus antigenemia (longer than 1 month), whereas 14 of 22 nonvaccinated control cats developed persistent viremia. In field tests, 2,770 cats from 6 states were vaccinated and observed. Postvaccinal reactions were not observed.

Research and development of unconventional systems for immunization.

The problems raised by the ever expanding world population justify the work of USAID (U.S. Agency for International Development). Continual efforts must be made to develop and efficiently operate methods of control of the microbial and parasitic infections which menace our sources of protein. This programme includes immunization, technical methods in bacterial and viral genetics to obtain attenuated strains, and improvements in production, preservation and distribution of preparations. An example of an unconventional but promising system of application is the pilot study recently begun in the Missouri-Mississippi River region.

Physical, chemical and biological characteristics of two bovine enterovirus plaque variants.

Large plaque (4LP) and small plaque (4SP) variants were derived from a parent bovine virus strain by serial plaque passage. Both 4LP and 4SP were resistant to chloroform and stabilized at 50 degrees C for one hour by 1.0 M magnesium chloride. Both 4LP and 4SP had buoyant densities in cesium chloride of 1.36 gm/ml. Antigenically, 4LP and 4SP were reciprocally cross neutralizable. The nucleic acid of 4LP was shown to be ribonucleic acid (RNA) by resistance of its infectivity to deoxynuclease (DNase) but not ribonuclease (RNase) and by increased incorporation of [(3)H]-uridine into cytoplasmic RNA in cells of virus infected cultures. In growth characteristics, both 4LP and 4SP had maximum adsorption times of 75 to 90 minutes but 4LP had more rapid replication and release rates and yielded nearly twice as many infectious units per cell as 4SP. The differences in growth properties correlated directly with the differential in plaque diameter which was 40-50%.

Interleukin 2 acts as an adjuvant to increase the potency of inactivated rabies virus vaccine.

Interleukin 2 (IL-2) occupies a central position in the cascade of events involved in the immune response. We were interested in determining whether IL-2 could function as an adjuvant to vaccination, to increase the immune response to vaccine immunogens. Using the National Institutes of Health test for rabies vaccine potency, we found that daily systemic administration of IL-2 in conjunction with inactivated rabies virus can increase the potency of vaccination in outbred mice at least 25-fold, as measured by survival following challenge with virulent rabies virus. Enhanced protection is not correlated with an increase in virus-neutralizing antibody titers, and we suggest that IL-2 acts to increase the cellular immune response to vaccination.