4063
In contrast, Spi-B is expressed exclusively in lymphoid cells and can be detected in early fetal thymus and spleen .
 lymphoid cells, Spi-B
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 lymphoid cells, Spi-B