Table 2.

Summary of checkpoint protein expression by pediatric tumor type

Tumor Type	CTLA-4	PD-1/PD-L1	CD200	IDO	References
Extracranial Solid Tumors
Ewing Sarcoma	ND	-/++/+++	ND	ND	(38-40)
Hodgkin’s Lymphoma	ND	ND	ND	+++	(71)
Non-Hodgkin’s Lymphoma	ND	+++	ND	ND	(40)
Neuroblastoma	+++	-/+/+++	+++	+++	(28), (38, 40, 42, 45), (58), (63)
Osteosarcoma	+++	++/+++	ND	+++	(28), (38, 47) , (69)
Retinoblastoma	ND	+++	ND	ND	(44)
Alveolar RMS	ND	+++	ND	ND	(38)
Embryonal RMS	+++	++	ND	ND	(28), (38)
Wilms, favorable	ND	+	ND	ND	(41)
Wilms, anaplastic	ND	++	ND	ND	(41)
Intracranial Solid Tumors
Ependymoma	ND	ND	+++	ND	(59)
Germinoma	ND	+++	ND	ND	(42)
Glioblastoma	ND	++	ND	ND	(40)
Medulloblastoma	ND	-/+++	ND	ND	(40)

Checkpoint protein expression was graded as follows:

^-, no expression;

⁺, 1-19% of tumors tested;

⁺⁺, 20-59% of tumors tested;

⁺⁺⁺, 60-100% of tumors tested.

ND; no data. RMS; rhabdomyosarcoma.