Here is the reference,
Acta Haematol. 2015;133(1):83-8. doi: 10.1159/000362356. Epub 2014 Aug 23.
High percentage of regulatory T cells before and after vitamin B12 treatment in patients with pernicious anemia.
Watanabe S1, Ide N, Ogawara H, Yokohama A, Mitsui T, Handa H, Koiso H, Tsukamoto N, Saitoh T, Murakami H.
Thank you for providing the reference to your previous question.
This study cannot be extrapolated to people with HIV who do not have anemia. Patients with anemia may have low blood levels of B-12 and/or iron, so normalizing these levels may provide benefits. B-12 supplementation in B-12 normal patients has not been proven to improve immune markers.