If human CD8T cell was injected intravenously into someone could it destroy their orexin receptors?

This is the study you're referencing, correct?

Bernard-Valnet R, Yshii L, Queriault C, Nguyen XH, Arthaud S, Rodrigues M, et al. CD8 T cell-mediated killing of orexinergic neurons induces a narcolepsy-like phenotype in mice. Proc Natl Acad Sci USA. (2016) 113:10956–61. doi: 10.1073/pnas.1603325113

It's possible, but hasn't been tested (from the likes of it, given what I've researched). There are orexin-producing neurons in the human brain, located predominantly in the perifornical area and lateral hypothalamus, so it is likely. According to Wikipedia, "there is considerable similarity between the orexin system in the rat brain and that in the human brain." (see below)

Boss C, Roch C (August 2015). "Recent trends in orexin research--2010 to 2015". Bioorganic & Medicinal Chemistry Letters. 25 (15): 2875–87. doi:10.1016/j.bmcl.2015.05.012. PMID 26045032.

Yes that’s the one! I can’t post links because my account is too new! If it was injected intravenously could it still cross the blood brain barrier?

Are you asking if injected CD8 cells can cross the blood-brain barrier? Yes.

"Here, we show that selective traffic of antigen-specific CD8 T cells into the brain occurs in vivo and is dependent on luminal expression of major histocompatibility complex (MHC) class I by cerebral endothelium. After intracerebral antigen injection, using a minimally invasive technique, transgenic CD8 T cells only infiltrated the brain when and where their cognate antigen was present."

https://pubmed.ncbi.nlm.nih.gov/17682068/