## 4 Discussion
It was already shown that mice injected with DCs transduced ex vivo with hAdV5-expressing \(\beta\)gal, elicited mainly IgG2a antibodies, while vaccination with hAdV5-\(\beta\)gal transduced myoblasts elicited a more balanced Ab response with an IgG1/IgG2a ratio similar to that induced by direct vaccination with hAdV5-\(\beta\)gal [52]; thus, it is likely that CoroVaxG.3 is inducing a more balanced immune response due to its enhanced tropism for muscle cells. In acute and convalescent COVID-19 patients, it has been observed that the presence of T cell responses is associated with reduced disease [53; 54; 55], suggesting that SARS-CoV-2-specific T cell responses may be important for the control and resolution of the primary SARS-CoV-2 infection [56]. Preclinical studies in macaques have shown that both neutralizing antibody titers and Fc functional antibody responses correlated with protection [57; 58] and that purified IgG from convalescent animals, in the absence of cellular and innate immunity, effectively protected naive recipients against a challenge with SARS-CoV-2 [59]. However, in the setting of waning and subprotective antibody titers, cellular immune responses were critical for rapid virological control. Through CD8 depletion studies, it was shown that cellular immunity, especially CD8+ T cells, contributed to the protection against rechallenge with SARS-CoV-2 [56]. The present data show that CoroVaxG vaccines induced a rapid and long-lasting cellular immune response, as characterized by the IFN-\(\gamma\) production and proliferation of memory CD8+ T cells, upon re-stimulation with SARS-CoV-2 peptides. Ex vivo stimulated splenocytes obtained from naive mice, or from mice injected with the empty vector, and non-stimulated splenocytes obtained from vaccinated mice exhibited basal levels of non-specific CD8+ memory cells consistent with aged mice [60; 61]. [PERSON] et al. [62] showed that both CD62 Llow and CD62 Lhigh memory cell subpopulations contributed to the recall responses to Sendai virus infection. However, the relative contributions of these subpopulations changed over time: CD62 Llow cells dominated at early time points, whereas CD62 Lhigh cells dominated at later time points. Consistent with this, we observed that the ex vivo stimulation of vaccinated mice splenocytes with Spike peptides induced a long-term increase in the TCM subpopulation. A correlate of protection that allows for the evaluation of vaccine efficacy based on immune readouts has been sought since the beginning of COVID-19 vaccine development. Recent studies suggest that neutralizing antibodies could serve this purpose and are, therefore, the main parameter that might help to predict the success of a vaccine candidate [63]. CoroVaxG.3 was able to elicit neutralizing antibodies at levels similar to those previously reported in preclinical animal models, and those nAbs were stable in the long term. Moreover, studies with pseudoviruses and the authentic SARS-CoV-2-containing variant substitutions suggested that the neutralizing ability of the antibodies in sera raised after CoroVaxG.3 vaccination is only slightly reduced but overall largely preserved against the B.1.1.7, P.1 and B.1.617.2 lineages that are VOC-prevalent in Latin America [64]. This mild reduction in neutralization by a single dose of CoroVax.G3 vaccine-raised sera against the VOC is in the same range as that observed for sera of patients who received mRNA or adenoviral vector vaccines [65; 66; 67]; interestingly, one dose of the Pfizer or the Astra Zeneca vaccines induced almost undetectable levels of neutralizing antibodies against Delta [68]. The dose chosen for preclinical immunogenicity studies was comparable to those used for other COVID-19 adenoviral-based vaccines in mice [43; 45; 69] and matched the range generally used for this kind of vaccines [70].