Recall interferon-γ responses against Coccidioides are a surrogate marker for vaccine response in dogs

To develop an interferon γ (IFN-γ) recall assay to detect a T-cell response following vaccination because antibody is seldom detected in Δcps1-vaccinated dogs.

Peripheral blood mononuclear cells were collected from naturally infected dogs with a history of coccidioidomycosis or dogs from a nonendemic area. Two- to 5-month-old Beagles were vaccinated 2 to 4 times up to 28 days apart with live, avirulent Δcps1 and bled on study days 42, 68, or 90. Peripheral blood mononuclear cells were stimulated with Δcps1 and stained to detect CD4+ T-cell IFN-γ expression. The percentage of CD4+IFN-γ+ T cells compared to unstimulated baseline was calculated for each dog.

All 5 naturally infected dogs with coccidioidomycosis had T-cell IFN-γ responses, and the 2 unexposed nonendemic dogs did not. Fourteen of 15 dogs vaccinated with Δcps1 had recall IFN-γ responses. Subcutaneously vaccinated dogs (n = 5) had a mean 1.85-fold increase in IFN-γ over baseline, whereas IM-vaccinated dogs (n = 10) were a mean of 6- to 10-fold higher. The percentage of CD4+IFN-γ+ cells was higher from restimulated cells compared to baseline in both SC- and IM-vaccinated dogs (SC twice [n = 5]: 95% CI, 0.001 to 0.543; IM twice [n = 5]: 95% CI, 0.9734 to 1.948; IM 4 times [n = 5]: 95% CI, 1.207 to 5.083).

The T-cell IFN-γ recall assay of peripheral blood mononuclear cells from vaccinated dogs detects a cell-mediated immune response to the Δcps1 vaccine.

This assay has potential utility as a surrogate marker for vaccine-induced immunity.