Autolus, which is developing next-gen cancer immunotherapies, had originally set out to raise US$100.8mln through the issue of 4.2mln American Depositary Shares (ADS) at US$24.00 apiece.
But it ended up issuing 4.83mln ADS at the same price to raise US$109.0mln.
As part of the offering, Arix agreed to invest US$5mln, keeping its stake in Autolus at 7.5%, which is currently valued at US$94mln (£72mln).
Speaking last week, Arix chief executive Joe Anderson said: “Our investment in Autolus demonstrates our strategy to build world-leading biotech companies through the provision of flexible, long term capital.
“We believe Autolus is at the forefront of a revolution in cancer treatment and that its innovative approach to T-cell programming has the potential to offer life-changing therapies for patients.”