Table 1 Important definitions associated with TCR diversity indices.

∙ Gini coefficient: inequality of a system or frequency distribution of different TCRs with values ranging between 0 (maximum diversity with perfect equality) to 1 (maximum unevenness)

∙ Shannon entropy & diversity index: a measure of the randomness within the system, takes into account both species richness and evenness, rises with increase in number of TCRs and evenness of their abundance with 0 representing no diversity. There is no upper limit to the value of Shannon diversity index

∙ Simpson’s diversity index, Ds: measures the probability that sequences randomly selected from a sample will belong to different T cell clonotype (0 = system with no diversity, 1 = system with high diversity)

∙ Inverse Simpson’s diversity index, 1/(1-Ds): is inverse of Simpson’s Diversity index (1 = system with no diversity, increasing value = increase in the diversity)