Key Inclusion Criteria:
* Histologically or cytologically confirmed diagnosis of stage 3 or 4 NSCLC, as per American Joint Committee on Cancer (AJCC) staging system (8th edition).
* Age 18 years or older at the time of informed consent
* Life expectancy \>12 weeks
* Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
* Have at least one measurable lung lesion per RECIST v1.1 at Screening
* Subject is receiving Keytruda or eligible to receive Keytruda
Key Exclusion Criteria:
* Not fully recovered from prior surgery or radiotherapy, including all radiation-related toxicities
* The subject is pregnant, nursing, or plans to become pregnant during study treatment and through three months after the last dose of KB707
* Have known history of positive human immunodeficiency virus (HIV 1/2)
* Subject has active brain metastases or leptomeningeal metastases
* Subject has a known additional malignancy that is progressing or requires active treatment
* Prior anti-PD-1/PD-L1 therapy was intolerable and required discontinuation of treatment
