But despite it all, he calls himself the "lucky one" as he now walks cancer-free, thanks to the groundbreaking CAR-T cell therapy, available only in the US and more recently Europe.
The problem was he had to travel more than 15,000km and had to raise more than $1m to get it.
"Most people don't get so lucky and because I was I feel like I owe it to society to do everything I can to bring it to New Zealand so others can have that same chance of survival as I did."
Second generation CAR-T therapies were licensed for use in the US and Europe for certain types of leukaemia and lymphoma.
New Zealand's Malaghan Institute planned to go a step further by developing a third generation CAR-T therapy, hoped to be more effective and easier to deliver.
The therapy worked by taking the immune cells - known as the T cells - out and genetically engineering them into "killer cells" before inserting them back into the blood.
Another Aucklander, Kurt Brunton, flew to the US earlier this week to undergo the same treatment. He too, faced the same challenges as Downs.
Head researcher, Robert Weinkove, said there were about 50 New Zealanders with non-Hodgkin lymphoma who became terminal every year.
"CAR-T therapy won't work for all of those patients but there is a lot of research suggesting the therapy could be used to treat other diseases as well as lymphoma and leukaemia."
Weinkove said this was extremely exciting stuff that opened the door for many more studies.
"Rather than having everything made overseas, we are actually manufacturing almost from scratch locally in New Zealand that gives us a flexible platform to allow us to generate other types of CAR-T cells therapies in the future."
Downs has pledged $1m that he hopes will be raised in less than a year.
Patients are advised to talk with their doctors about their treatment options to see if they were eligible. Recruitment for the trial will be announced at a later date.