About PD-1
Programmed cell death protein 1 (PDCD1) is an immune-inhibitory receptor expressed in activated T cells; it is involved in the regulation of T-cell functions, including those of effector CD8+ T cells. In addition, this protein can also promote the differentiation of CD4+ T cells into T regulatory cells. PDCD1 is expressed in many types of tumors including melanomas, and has demonstrated to play a role in anti-tumor immunity. Moreover, this protein has been shown to be involved in safeguarding against autoimmunity, however, it can also contribute to the inhibition of effective anti-tumor and anti-microbial immunity. [provided by RefSeq, Aug 2020]

About PE-Cy5.5
PE-Cyanine®5.5 (PE-Cy5.5) is a red-emitting tandem fluorophore that combines phycoerythrin (PE) and Cy5.5. The donor molecule, PE can be excited by the 488-nm blue, 532-nm green, or 561-nm yellow-green laser and and transfers energy to the acceptor molecule, Cy5.5. PE-Cy5.5 has an excitation peak at 496 nm and an emission peak at 695 nm.