Feline Calicivirus Can Tolerate Gross Changes of Its Minor Capsid Protein Expression Levels Induced by Changing Translation Reinitiation Frequency or Use of a Separate VP2-Coding mRNA

Caliciviruses use reinitiation of translation governed by a ‘termination upstream ribosomal binding site’ (TURBS) for expression of their minor capsid protein VP2. Mutation analysis allowed to identify sequences surrounding the translational start/stop site of the feline calicivirus (FCV) that fine tune reinitiation frequency. A selection of these changes was introduced into the infectious FCV cDNA clone to check the influence of altered VP2 levels on virus replication. In addition, full length constructs were established that displayed a conformation, in which VP2 expression occurred under control of a duplicated subgenomic promoter. Viable viruses recovered from such constructs revealed a rather broad range of VP2 expression levels but comparable growth kinetics showing that caliciviruses can tolerate gross changes of the VP2 expression level.     

In Vivo Neutralization of α-Cobratoxin with High-Affinity Llama Single-Domain Antibodies (VHHs) and a VHH-Fc Antibody

Small recombinant antibody fragments (e.g. scFvs and V_HHs), which are highly tissue permeable, are being investigated for antivenom production as conventional antivenoms consisting of IgG or F(ab’)₂ antibody fragments do not effectively neutralize venom toxins located in deep tissues. However, antivenoms composed entirely of small antibody fragments may have poor therapeutic efficacy due to their short serum half-lives. To increase serum persistence and maintain tissue penetration, we prepared low and high molecular mass antivenom antibodies. Four llama V_HHs were isolated from an immune V_HH-displayed phage library and were shown to have high affinity, in the low nM range, for α-cobratoxin (α–Cbtx), the most lethal component of Naja kaouthia venom. Subsequently, our highest affinity V_HH (C2) was fused to a human Fc fragment to create a V_HH2-Fc antibody that would offer prolonged serum persistence. After in planta (Nicotiana benthamiana) expression and purification, we show that our V_HH2-Fc antibody retained high affinity binding to α–Cbtx. Mouse α–Cbtx challenge studies showed that our highest affinity V_HHs (C2 and C20) and the V_HH2-Fc antibody effectively neutralized lethality induced by α–Cbtx at an antibody:toxin molar ratio as low as ca. 0.75×:1. Further research towards the development of an antivenom therapeutic involving these anti-α-Cbtx V_HHs and V_HH2-Fc antibody molecules should involve testing them as a combination, to determine whether they maintain tissue penetration capability and low immunogenicity, and whether they exhibit improved serum persistence and therapeutic efficacy.     

Effect of Penicillin on Staphylococcus aureus Cultivated at High Atmospheric Pressure

Staphylococcus aureus showed decreased penicillin susceptibility at high atmospheric pressure (0.3% O₂ in He, 1,000 psi). High pressure may have protected the bacteria by osmotic stabilization.     

Purification of deoxycytidine kinases from two P815 murine neoplasms and their separation from deoxyguanosine kinase

Deoxycytidine kinase, which catalyzes the phosphorylation of deoxycytidine and 1-βd-arabinofuranosylcytosine (Ara-C) at the 5′-position, has been extracted and extensively purified from a murine neoplasm P815, either sensitive (P815) or resistant (P815/ Ara-C) to 1-β-d-arabinofuranosylcytosine. Gel filtration and ion-exchange chromatography were used to accomplish the purification. The purified enzyme exhibited a single band upon disc electrophoresis. During the extraction procedure an enzyme catalyzing the phosphorylation of deoxyguanosine and deoxyadenosine was successfully separated for the first time from deoxycytidine kinase. The K_m values and turnover numbers with deoxycytidine as phosphate acceptor for the kinase from P815 cells sensitive to 1-β-darabinofuranosylcytosine and that from P815 cells resistant to the drug are 9.3 μm, 4.7 × 10⁶/min and 15.4 μm, 8.0 × 10⁴/min, respectively.     

Memory T cells are uniquely resistant to melanoma-induced suppression

We have previously observed that in vivo exposure to growing melanoma tumors fundamentally alters activated T cell homeostasis by suppressing the ability of naïve T cells to undergo antigen-driven proliferative expansion. We hypothesized that exposure of T cells in later stages of differentiation to melanoma would have similar suppressive consequences. C57BL/6 mice were inoculated with media or syngeneic B16F10 melanoma tumors 8 or 60 days after infection with lymphocytic choriomeningitis virus (LCMV), and splenic populations of LCMV-specific T cells were quantified using flow cytometry 18 days after tumor inoculation. Inoculation with melanoma on post-infection day 8 potentiated the contraction of previously activated T cells. This enhanced contraction was associated with increased apoptotic susceptibility among T cells from tumor-bearing mice. In contrast, inoculation with melanoma on post-infection day 60 did not affect the ability of previously established memory T cells to maintain themselves in stable numbers. In addition, the ability of previously established memory T cells to respond to LCMV challenge was unaffected by melanoma. Following adoptive transfer into melanoma-bearing mice, tumor-specific memory T cells were significantly more effective at controlling melanoma growth than equivalent numbers of tumor-specific effector T cells. These observations suggest that memory T cells are uniquely resistant to suppressive influences exerted by melanoma on activated T cell homeostasis; these findings may have implications for T cell–based cancer immunotherapy.