Challenges in confirming a varicella outbreak in the two-dose vaccine era

BACKGROUND

A second dose of varicella vaccine was recommended for U.S. children in 2006. We investigated a suspected varicella outbreak in School District X, Texas to determine 2-dose varicella vaccine effectiveness (VE).

METHODS

A varicella case was defined as an illness with maculopapulovesicular rash without other explanation with onset during April 1-June 10, 2011, in a School District X student. We conducted a retrospective cohort in the two schools with the majority of cases. Lesion, saliva, and environmental specimens were collected for varicella-zoster virus (VZV) PCR testing. VE was calculated using historic attack rates among unvaccinated.

RESULTS

In School District X, 82 varicella cases were reported, including 60 from Schools A and B. All cases were mild, with a median of 14 lesions. All 10 clinical specimens and 58 environmental samples tested negative for VZV. Two-dose varicella vaccination coverage was 66.4% in Schools A and B. Varicella VE in affected classrooms was 80.9% (95% CI: 67.2-88.9) among 1-dose vaccinees and 94.7% (95% CI: 89.2-97.4) among 2-dose vaccinees in School A, with a second dose incremental VE of 72.1% (95% CI: 39.0-87.3). Varicella VE among School B students did not differ significantly by dose (80.1% vs. 84.2% among 1-dose and 2-dose vaccinees, respectively).

CONCLUSION

Laboratory testing could not confirm varicella as the etiology of this outbreak; clinical and epidemiologic data suggests varicella as the likely cause. Better diagnostics are needed for diagnosis of varicella in vaccinated individuals so that appropriate outbreak control measures can be implemented.

The Walker 256 carcinoma: a cell type inherently sensitive only to those difunctional agents that can form DNA interstrand crosslinks

The Walker 256 rat tumour has been maintained in vivo for over 60 years and until recently was used as a primary screen for new antitumour agents. This screen was particularly useful in identifying difunctional alkylating agents as potentially useful anticancer agents and it would seem that the Walker tumour is composed of cells sensitive towards this type of agent. A cell line (WS) established from the Walker tumour retained the sensitivity of the tumour towards difunctional agents and we have examined its phenotype in comparison to a derived, resistant, cell line (WR). The response of WR cells to a range of cytotoxic agents was similar to other established cell lines whilst WS cells were much more sensitive only towards difunctional reacting agents. There were no significant differences in the binding of these agents to the DNA of WS or WR cells. All the agents towards which WS cells showed sensitivity were, without exception, capable of reacting with DNA in Walker cells and forming DNA-DNA interstrand crosslinks. WS cells were not sensitive to busulphan, BCNU, CCNU or Me-CCNU but these agents did not produce interstrand crosslinks in the DNA of either WS or WR cells. Thus WS cells are intrinsically sensitive to specific DNA damage and this is probably a DNA interstrand crosslink. Hybrid cells produced by fusion of WS with WR cells lacked the inherent sensitivity of the WS cells towards cisplatin; sensitivity was therefore a recessive characteristic. Transfection of WS cells with human DNA also gave rise to 2 cisplatin-resistant clones, although it could not be ascertained if these clones were true transfectants or revertants. The survival of these resistant clones, after treatment with cisplatin, was about the same as WR cells a finding which would be consistent with complementation by a transferred gene or reversion of a single gene defect in WS cells. In their sensitivity only to difunctional compounds and lack of an apparent DNA excision repair defect the phenotype of Walker cells strongly resembles those cells from human patients suffering from Fanconi's anaemia and also of yeast snm1 mutant cells. The mechanisms giving rise to this failure to tolerate specific DNA damage (which seems to involve the inability to recover from the initial inhibition of DNA synthesis and may involve a single defect of a gene involved in the late steps of crosslink repair), do not involve drug uptake, drug binding to DNA, cell size, cell doubling time or DNA excision repair.

Properties of mer- HeLa cells sensitive or resistant to the cytotoxic effects of MNU; effects on DNA synthesis and of post treatment with caffeine

A line of HeLa cells was shown to be particularly sensitive to N-methyl-N-nitrosurea (MNU) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), but not to a variety of other cytotoxic agents. A resistant line (designated HeLa/A22), was derived by treating HeLa cells repeatedly with MNU. Both the sensitive (HeLa) and resistant (HeLa/A22) cells have a mer- phenotype based both on their reduced rates of loss of O6-methylguanine (O6-MeG) from DNA and their low levels of the enzyme O6-methylguanine methyltransferase (MT). HeLa cells are therefore sensitive to unrepaired O6-MeG in DNA while the HeLa/A22 cells are resistant to unexcised O6-MeG and thus the A22 cells have the mer-rem+ phenotype. MNU produced an immediate dose-dependent inhibition of DNA synthesis in cultures of both sensitive and resistant cells which increased with time until about 4 h after treatment. DNA synthesis then recovered to near control rates in both sensitive and resistant cells before then exhibiting a progressive decrease after about 24 h. DNA synthesis was more depressed at these late times after treatment in cultures of sensitive cells than in those of similarly-treated resistant cells. DNA synthesis remained depressed in sensitive cells but recovered 3 days after treatment in resistant cells. Post treatment incubation of MNU-treated HeLa cells with caffeine did not increase the toxic action of MNU. In contrast, post treatment of the resistant HeLa/A22 cells with caffeine resulted in a dramatic increase in the toxic effects of a higher equitoxic dose of MNU. The depressed rate of DNA synthesis observed in both cell lines after high doses of MNU was partially reversed by post treatment with caffeine in both sensitive and resistant cells. These observations can be interpreted in terms of the effects of caffeine on DNA replication in treated cells.

The independent action of radiation and cisplatin on the survival or recovery of human normal or tumour cells in vitro or in vivo

Recovery from radiation- or cisplatin-induced lethal damage has been studied in euoxic normal human foetal lung fibroblasts (HFL cells) that remain viable for at least 20 days in plateau-phase culture. After a 1 hour treatment with cisplatin the half-time of recovery was about 2 days. By contrast recovery after radiation was more rapid with half-times of approximately 10 h. There was no further measurable recovery after 2 days. With either agent the recovery ratios (RR) were dose-dependent but recovery (following treatment with equitoxic doses of the two agents) was appreciably greater after cisplatin (RR approximately 123 after 40 microM for 1 h) than after radiation (RR approximately 15 after 900 cGy). When radiation (900 cGy) was combined with cisplatin (40 microM for 1 h) the cell survival, measured at 5 days or later times after the treatments, was not significantly less than that predicted by the additive, independent effects of both agents (calculated as the product of their respective effects on cell survival) irrespective of whether cisplatin was given 1 h before, during or for 1 h immediately after radiation. In euoxic, exponentially growing HFL or HeLa cells there was no evidence that combinations of cisplatin and radiation gave more than additive toxic effects in the protocols tested. The combined effects of cisplatin or carboplatin and whole-body irradiation given 45 min later, on human melanoma cells (assessed by their colony-forming abilities in vitro) growing in thymectomised mice, were essentially the same as that predicted by the additive, independent effects of the two agents.

The effect of monofunctional or difunctional platinum adducts and of various other associated DNA damage on the expression of transfected DNA in mammalian cell lines sensitive or resistant to difunctional agents

The effects of introducing various DNA damage into pSV2gpt DNA on the subsequent expression of xanthine guanine phosphoribosyltransferase (XGPRT), after its transfection into two Walker 256 cell lines, one which is inherently sensitive only to difunctional agents while the other shows a normal sensitivity, have been examined. Both the sensitive (WS) and the relatively resistant (WR) cell lines were shown to be equally capable of both ligation of DNA double-strand breaks (although the efficiency varied with the actual site of the break) introduced into pSV2gpt and homologous recombination of pSV2gpt fragments (recombination events are thought to be important in the repair of DNA-DNA interstrand crosslinks). Reacting the plasmid with either the difunctional platinum compound, Cisplatin, or the monofunctional reacting Pt(Dien) caused a dose-dependent decrease in the subsequent expression of XGPRT. This decrease was about the same with either agent in either cell line when expressed as a function of dose of drug. However, when the actual binding of platinum to DNA by these compounds was measured, a large difference (due to the higher specific binding of Pt(Dien) to DNA) in the effects of the difunctional, as opposed to the monofunctional agent, was apparent and this was a reflection of the relative cytotoxicities of these compounds towards mammalian cells. Although at doses of Cisplatin equitoxic to WS and WR cells 20-fold less Pt is bound to the DNA of WS cells, no significant difference was seen on the expression of pSV2gpt, reacted with this agent, between WS or WR cells. Based upon a knowledge of the proportions of adducts formed in DNA reacted with Cisplatin, the lesion that inactivates expression of XGPRT was probably the intrastrand crosslink and it was calculated that due to the size of the plasmid, the interstrand crosslink was unlikely to be present at these inactivating doses. It is suggested that the inherent sensitivity of WS cells only to difunctional agents is due to their response to such relatively rare lesions such as a DNA-DNA interstrand crosslink.

Differential arginine dependence and the selective cytotoxic effects of activated macrophages for malignant cells in vitro

Normal and neoplastic cells from 4 species (man, rat, mouse and hamster) were examined for their dependence on exogenous L-arginine in tissue culture. The malignant cells required a higher concentration of L-arginine in the medium than their normal counterparts (with similar doubling times) to maintain optimal proliferation. Complete arginine deprivation resulted in equal growth inhibition of normal and malignant cells, but more rapid cytolysis of the malignant cell. Deprivation of L-arginine, followed 24 h later by rescue with L-arginine, allowed normal cells to proliferate, but the reproductive capacity of the malignant cells was irreversibly impaired. Since the cytotoxic activity of LPS-activated macrophages was associated with the release of arginase and was abrogated by excess L-arginine, it is suggested that the biological basis for the selective effects of such macrophages may reside in the L-arginine dependence of the target cells.

Activated macrophages release a factor which lyses malignant cells but not normal cells

When rat macrophages are activated by exposure to bacterial endotoxin they acquire the capacity to lyse sarcoma cells in tissue culture. Although showing no immunological specificity this lytic effect was only detectable on malignant cells; normal cells were unaffected. This tumor-selective lytic effect is mediated by a labile supernatant product.

Development of specific cell-dependent antibody during growth of a syngeneic rat sarcoma

A micro-cytotoxicity assay was adapted for the detection of cell-dependent antibodies (CDA). Using normal rat spleens as the source of effector cells such CDA activity was readily demonstrable in allo-immune sera tested on cultured sarcoma cells. The same technique was then used to examine for tumour specific antibodies in the sera of Hooded rats bearing a "non-immunogenic" syngeneic metastasizing sarcoma. During the early stages of tumour growth, at Days 7 and 14, tumour specific CDA cytotoxicity was detectable at high titres. By Day 21, however, this activity had completely disappeared from the serum. This cell-dependent cytotoxicity was tumour specific in that it did not kill cells from an unrelated syngeneic sarcoma, and the activity was probably confined to immunoglobulin G as detected by molecular weight separation techniques. Following tumour amputation at Day 21, this type of specific antibody activity rapidly re-appeared in the serum. The presence of tumour specific CDA showed an inverse correlation with the presence of specific inhibitors of cell-mediated immunity in the same sera. At no stage in tumour growth could complement-dependent cytotoxicity be detected in tumour bearing rat sera.It is concluded that cell-dependent cytotoxic activity is not associated with conventional complement dependence, that this CDA type of assay is exquisitely sensitive and is suitable for the detection of anti-TSTA antibodies in tumour bearing rats.The possible significance of CDA activity in syngeneic tumour immunity is discussed briefly. The results suggest that the role of humoral immune mechanisms in host resistance to tumour growth needs re-appraisal.

Serum mediated inhibition of the immunological reactions of the patient to his own tumour: a possible role for circulating antigen

In a microcytotoxicity assay the lymphocytes from cancer patients were tested on autologous and allogeneic tumour cells in vitro. In patients with a variety of tumours, extensive washing of the lymphocytes from those cases with advanced disease was found to greatly enhance their specific cytotoxic effects. This specificity was restricted to autologous tumour cells and allogeneic cells of similar histological origin. This cross-reacting cytotoxicity was not, however, universal, especially in cases of malignant melanoma. The cytotoxicity evoked by washing was abolished by the addition of the patient's serum. This serum effect showed a similar specificity to that found for lymphocyte cytolysis. The effect of washing, and the specific inhibitory effect of serum, was not detectable in early cases of primary malignant melanoma. The serum component responsible for inhibiting lymphocyte cytotoxicity had no detectable affinity for the target cells and appears to act on the lymphocyte surface, implying that tumour antigen may well be implicated.