When you say combo therapies - Like DC VAX and PDL-1?
DC therapy has actually been proven to work. Provenge had to beat it's own frozen self and this was only pulsed with I believe 1 antigen. Still antigen spread and immune memory was actually observed.
IMUC used multiple antigens and the therapy appeared to work for a subset of patients that expressed more of these antigens. Not all patients and tumors are alike - Cancer is heterogeneous
DCVax is a tumor lysate and theoretically is pulsed with every available antigen specific to the tumor of the individual patient and not a pre determined subset of antigens selected by a doctor. They are letting the DC cells determine the antigens.
DCVax may not be the entire answer but it provides the playbook to the immune system. Other immune boosters and checkpoint inhibitors may increase the effectiveness. If you have the playbook but not enough players or the players are being handcuffed(PD), then it will not be as effective. The Death Star may need its shield to be removed before it can be attacked....and DCvax would not limit a person from other treatments.