Lymphocytic Choriomeningitis virus. I. Concentration and purification of the infectious virus.

Two procedures for the purification of infectious lymphocytic choriomeningitis virus from cell culture fluid have been developed. If large quantities of very pure virus are to be prepared, infected L cells are maintained with a medium supplemented with calf serum, the proteins of which have been largely removed by pretreatment with polyethylene glycol. Two days after infection of the cultures, the media are collected and the virus is concentrated by treatment with polyethylene glycol 40,000. Purification with a 10,000-fold increase of specific infectivity is achieved with steric chromatography on controlled-pore glass beads with pore sizes of 42 to 44 nm and centrifugation in density gradients prepared with amido trizoate. An alternative method begins with precipitation of the virus from infected cell cuture medium with zinc acetate, followed by controlled-pore glass chromatography and density centrifugation in a discontinuous sucrose gradient. Purification thus obtained is 200-fold in terms of specific infectivity.     

Foamy virus vectors.

Human foamy virus (HFV) is a retrovirus of the spumavirus family. We have constructed vectors based on HFV that encode neomycin phosphotransferase and alkaline phosphatase. These vectors are able to transduce a wide variety of vertebrate cells by integration of the vector genome. Unlike vectors based on murine leukemia virus, HFV vectors are not inactivated by human serum, and they transduce stationary-phase cultures more efficiently than murine leukemia virus vectors. These properties, as well as their large packaging capacity, make HFV vectors promising gene transfer vehicles.     

Adeno-associated virus vectors.

Adeno-associated virus is a human parvovirus that integrates its DNA genome into host cell chromosomes with very high efficiency. This suggests that adeno-associated virus may be a useful vector for human gene therapy. Interest in adeno-associated virus vectors increased greatly in the last year following reports that adeno-associated virus genome integration may be site specific and occur at preferred sites in the human genome. Several genes relevant to the treatment of genetic or infectious diseases have been expressed in adeno-associated virus vectors in vitro.     

B.K. virus haemagglutinin.

Among the widely applied buffered media, the HSAG (hepes-salt-albumin-gelatin) medium at pH 5.75--6.25 was found to be the most favourable for B.K. virus haemagglutinin titration. The optimum temperature was at 4 degrees C. The haemagglutinin was not affected by temperatures up to 37 degrees C, pHs between 5.5 and 9.5, and NaCl concentrations between 0.063 M and 2.56 M. When incubated at 56 degrees C, the haemagglutinin shows a time and pH dependent decline in titre. No significant time dependent titre fall occurred at 56 degrees C if NaCl molarity was varied between 1.31 and 2.56.     

Infantile gastroenteritis virus.

The authors demonstrated presence of virus particles of 55--75 nm manifesting morphological properties of the virus of infantile gastroenteritis (rotavirus, orbivirus, reo-like virus) by means of the electron microscopy, when investigating samples of stools of children sufferring from non-bacterial diarrheal diseases. Stool extracts were incubated with commercial gamma globulins or with convalescent sera provoking formation of extensive immunocomplexes. The complexes do not form when stool extracts are incubated with sera obtained from initial stages of the disease. This finding is an evidence of the presence of the virus in question among our population.     

Human immunodeficiency virus drug therapy and virus load.

Analysis of the short-term dynamics of human immunodeficiency virus (HIV) type 1 infection in response to drug therapy has elucidated crucial kinetic properties of viral dynamics in vivo (D. D. Ho et al., Nature 373:123-126, 1995; A. S. Perelson et al., Science 271:1582-1586, 1996; X. Wei et al., Nature 373:117-122, 1995). Here we investigated long-term changes in virus load in patients treated with a combination of lamivudine and zidovudine to identify principal factors responsible for the observed 10- to 100-fold sustained suppression of virus load in vivo. Interestingly, most standard accounts of virus dynamics cannot explain a large sustained reduction without shifting the virus very close to extinction. The effect can be explained by taking into consideration either (i) the immune response against HIV, (ii) the killing of uninfected CD4 cells, or (iii) the differential efficacies of the drugs in different cell populations.