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-Fire 640
PE-Fire™ 640 from Biolegend is a red-emitting tandem fluorophore that combines pycoerythrin (PE) and Fire™ 640. 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, Fire™ 640, which emitts light that can be captured with a 630/69 nm bandpass filter. PE-eF610 has an excitation peak at 565 nm and an emission peak at 639 nm. In spectral cytometry, this dye can be accurately unmixed from other dyes with highly overlapping spectral profiles, such as PE-Dazzle® 594 and PE-Cy5. PE-Fire™ 640 is recommended for labeling antigens that: (1) are expressed on a small subset (2) will be excluded from final analysis, and (3) require a bright signal but are not co-expressed with an antigen marked by a dye with overlapping spectra.