Brown was originally left out of the Elite Player Squad at the start of the season but his outstanding work in the line-out and brilliant defence in the wide channels has marked him down as a player with international prospects.
"I am really pleased - it's awesome," Brown said. There are a lot of quality locks around and I was really surprised to be included, especially after I was left out of the EPS squad at the start of the year.
"Squads change so often that I thought I still had a chance but it's still brilliant news. I just had to go away, get my head down, do my best for the club and concentrate on playing well.
"If I played well there, success would come off the back of it and hopefully it has. I look forward to this as a great opportunity in the autumn and hopefully build on it."
Brown is not solely a set-piece lock and since his arrival at Kingsholm from Bristol has re-developed himself into one of the most damaging defenders on the circuit.
He was joined in the squad by fellow forwards Phil Vickery - back after a season out injured - and James Forrester, who has impressed with his ability to widen his repertoire this season in the tight phases of the game.
Forrester was still able to make an impact against Northampton last Saturday, despite the fact he operated outside his natural environment.
"It's never good to really presume anything until you know for sure, but I am pretty chuffed to be included," he said. "There is a long way to go before the games so I suppose anything could happen - I just need to get my head down and work hard.
"I feel I am in better shape because I had a lot of trouble with my shoulder. I have worked hard to develop things highlighted to me and areas I needed to improve and I will carry that on."
Scrum-half Peter Richards, who joined the club from Wasps in the summer, has battled it out with Haydn Thomas for the number nine shirt and said: "It's come as a bit of a shock. There are obviously three scrum-halves in the squad and I may have my work cut out to make the matchday 22.
"But I am looking forward to the training week and hopefully I can make my mark. It's nice to know that after limited opportunities I have had this season, been able to make an impact.
"Haydn Thomas is a good player as well at Gloucester and I have enjoyed the challenge. Hopefully, when the squad is reduced, I will still be involved."
Simpson-Daniel, who made a try-scoring return against the Saints last weekend after an ankle injury, added: "I am obviously really, really pleased to be included again after my injury at the start of the season. Competition for places is massive and to make the first squad of 30 is important to me.
"I still have a long way to go to get full match fitness, but now I am back involved with Gloucester, England has come as a huge bonus for me at this stage."