Viral vaccines and antivirals: current use and future prospects.

The evolution of viral vaccines from the time of Jennerian prophylaxis to today's recombinant technology has been a continuing story of success. From the relatively crude or "first generation" vaccines for smallpox, rabies, and yellow fever followed a second and third generation of improved or new viral vaccines. The application of techniques for attenuating, inactivating, and partially purifying candidate viruses yielded safe, effective vaccines against influenza, poliomyelitis, measles, mumps, and rubella. With the advent of effective national immunization programs in the United States and other areas of the world to promote wide scale use of these vaccines, we have seen a dramatic decrease in incidence of the viral infections of childhood. The new biotechnology serves as the cornerstone for a fourth generation of vaccines and has already provided a licensed recombinant yeast human hepatitis B vaccine. The prospects for a wide spectrum of new or improved vaccines are highly encouraging, not only because of the recent technical advances but also because vaccine development has been recognized as a priority area of research. Under the National Institute of Allergy and Infectious Diseases' Program for Accelerated Development of New Vaccines, support is being provided for developmental vaccine studies with hepatitis A and B, influenza A and B, rabies, rotavirus, varicella, and respiratory syncytial virus (53). The outlook for antivirals is equally optimistic. The same technologies that have provided greater insight into the genetics and molecular biology of viruses and hence the means to fashion subunit or even synthetic vaccines have yielded data that can be applied to successful development of targeted antiviral compounds.

Cell culture models as ancillary tools in the isolation and characterization of mycoplasmas.

Since the late 1960s, there have been an increasing number of reports describing the isolation and identification of fastidious strains of Mycoplasma hyorhinis in cell cultures but not in conventional mycoplasma media, i.e., agar and broth. The application of those techniques normally used in studying viruses, i.e., infection of cell cultures coupled with the subsequent use of immunological and biological test procedures, has provided a reliable alternative procedure for M. hyorhinis detection. Major isolation surveys have revealed that as many as 60 to 80% of M. hyorhinis isolates from contaminated tissue cultures failed to grow in agar medium. Efforts to elucidate the mechanisms involved in failure of the cell culture-derived M. hyorhinis strain to grow in standard cell-free mycoplasma media are ongoing. Initial data indicated that extracts prepared from tissue cultures (BHK 21) and incorporated in Macpherson's broth and agar medium would permit growth of fastidious strains. Moreover, it appears that these strains are particularly sensitive to inhibition by yeast products often found in mycoplasma media. While M. hyorhinis appears to be unique with respect to its sensitivity to medium components, these fastidious strains are isolated with such frequency that the routine use of an indicator cell system is strongly recommended.

Monkey kidney cell growth optimization and poliovirus propagation in microcarrier culture.

Three monkey kidney cells lines Vero, LLC-MK2 and CV-1 were grown in microcarrier cultures. The carrier support was DEAE-Sephadex gel beads at low anion exchange capacity prepared according to a protocol developed at the Massachusetts Institute of Technology. The growth rate of the cells and the final cell density in microcarrier culture was dependent on the concentration of the beads in culture and on the size of the initial cell inoculum. The efficiency of the microcarrier culture system was compared to that of stationary and roller bottle cultures. The microcarrier culture system was applied to the propagation of polioviruses in the three established monkey kidney cell lines and the yields were compared with those obtained in roller bottle and stationary cultures. The yield of the three types of polioviruses in the various cell lines and culture systems was similar. The use of the microcarrier culture system for anchorage-dependent cells together with the use of continuously propagating cell lines offer great advantage for large-scale cultivation of poliovirus for the preparation of killed poliovirus vaccines.

Cell growth optimization in microcarrier culture.

Three monkey kidney cell lines and primary chicken embryo cells were grown in microcarrier culture. The carrier support was DEAE-Sephandex gel beads at low anion exchange capacity prepared according to a protocol developed at the Massachusetts Institute of Technology. The growth rate of the cells and the final cell density in microcarrier culture was dependent on the concentration of the beads in culture and on the size of the initial cell inoculum. A bead concentration of 1.0 to 2.0 mg of beads/ml of tissue culture medium and a cell inoculum of 20,000 cells/cm2 of bead surface appeared to be optimal. The efficiency of the microcarrier culture system was compared to that of stationary and roller bottle cultures. Stationary flasks gave cell densities about twofold higher than maximal densities in roller bottles and about threefold and twofold higher than cell densities in microcarrier culture at a bead concentration of 2.5 and 1.0 mg/ml, respectively. In terms of cell yield per milliliter of tissue culture medium, the microcarrier culture was superior to roller bottle and stationary cultures. An advantage of the microcarrier culture system is its suitability for scale up into large volume production units.

Control of measles and rubella through use of attenuated vaccines.

A summary report of the current status of morbidity and mortality associated with measles and rubella vis á vis immunization practices in the United States since these vaccines were licensed in 1963 (measles) and 1969 (rubella) is presented.

Review of existing vaccines for influenza.

The problems of producing and distributing influenza vaccines are described as well as effectiveness and adverse reactions. It appears that Guillain-Barré (GBS) is likely to be encountered with the use of any of the inactivated influenza vaccines.

Summary of clinical trials of influenza virus vaccines in adults.

Trials in approximately 3,900 adults were conducted with influenza A/New Jersey/76, A/Victoria/75, and B/Hong Kong/72 virus vaccines. Subjects were observed following a standard protocol, and serologic testing was performed in a single laboratory. The data indicate that prior experience of the population with earlier influenza viruses ("priming") is a determinant in response to vaccination. Thus, participants older than 25 years showed good serologic response following a single inoculation of A/New Jersey/76 virus, while younger persons responded poorly. Serological responses to A/Victoria/75 and B/Hong Kong/72 viruses were, in contrast, equally good in the younger and older adults. Whole-virus vaccines were measurably more reactive than split-virus vaccines, a finding more easily discernined in unprimed populations. In the unprimed persons, a single dose of split-virus vaccine was less immunogenic than a single dose of whole-virus vaccine. The presence of preexisting antibodies appeared to reduce systemic reactivity. For adequate immunization of a totally unprimed population, a single relatively large and reactive dose of whole-virus vaccine or two, properly spaced, smaller nonreactive doses of either whole-virus vaccine or split-virus vaccine would be required.

Detection of bovine viruses in fetal bovine serum used in cell culture.

This investigation employed a viral screening method detect endogenous bovine virus contaminants in commercially supplied fetal bovine serum. Fifty-one lots of fetal bovine serum from 14 suppliers were examined. Over 30% of the lots tested were found to contain bovine viruses; they included bovine virus diarrhea virus, parainfluenza type3-like virus, bovine herpesvirus-1, bovine enterovirus type 4, and an unidentified cytopathogenic agent. Of the 51 lots, 20 had been pretested by the suppliers and were considered to be free of known viral contaminants. Our viral screening methods revealed that five of these pretested lots, or 25%, contained endogenous bovine viruses.